FR2570693A3 - Refractory material for hot guniting - Google Patents

Abstract

In a material for hot guniting for the repair of refractory coatings, especially coatings of metallurgical containers, material of the type comprising at least two base products one of which acts as a refractory granulate and the other as a binder which melts at the temperature of spraying of the mixture, the material comprises a product capable of reacting at the spraying temperature with at least the binder when the latter is in the molten state, to form a solid compound which is more refractory than the binder.

Description

Refractory material * hot gunning area.

 The invention relates to hot gunning, therefore through a flame for the repair of refractory linings, in particular for metallurgical vessels such as converters.

 It is known that a material projecting through a flame must contain at least two types of constituents: the first constituent, the main aggregate, of the same nature as that of the material making up the coating to be repaired, remains solid when crossing the flame and constitutes the reinforcement of the sprayed product, the second constituent, the binder, voluntary addition or impurities present in the product, melts and serves as cement for the main aggregate.

The characteristics of the projected layers depend closely on the formation and the importance of the liquid phase, at the time of the projection. This liquid phase is essential for
- provide the product with good density, and therefore good resistance to corrosion, erosion, etc.,
- ensure high mechanical strength,
- ensure good adhesion,
- limit losses by rebounds.

 On the chemical composition of the liquid phase depends the overall refractoriness of the sprayed product (and therefore its lifetime).

 The composition of this binder and its melting temperature must be compatible with the temperatures developed in the burner.

 However if the melting temperature of the binder is too high ~~ it does not melt and the product does not settle on the wall.

 If it is too weak, the sprayed product melts correctly but its refractory properties are poor.

To reconcile these two opposite aspects, the most used means is the use of burners with the highest possible flame temperatures: propane / oxygen burners,
LPG / oxygen or better fuel / oxygen.

 The expected result is then obtained: the direct installation of a product comprising a liquid phase with high refractoriness.

 However, this method has a serious drawback: the use of flames at high temperature causes an extremely rapid rise in the wall to be repaired during projection.

 This results in internal stresses resulting in cracking and flaking of the coating, causing the projected layers to fall.

 The object of the invention is to propose a new design of the gunning material which allows satisfactory use at lower flame temperatures.

 This object is achieved by the fact that the proposed gunning material comprises a product capable of entering into reaction, at the projection temperature of the mixture, with at least the binder when the latter is in the molten state, to form after cooling a solid compound more refractory than the binder.

 In this type of material, the binder completely melts in the flame during the projection, then reacts with another component present in the product (main aggregate or additional additive), to form a new compound, more refractory, solid at the temperature d 'use.

 Given the types of coatings conventionally used, in particular in metallurgy, the aggregates are either aluminous (bauxite, tabular alumina, fused corundum), or magnesian (terrestrial magnesia, seawater or electrofused). Binders are compounds (silicates, phosphates, aluminates) of sodium or calcium.

In its most general form, the material of the invention therefore comprises three compounds
1. a refractory aggregate with a composition similar to that of the coating to be repaired. I1 remains solid during projection.

 2. a binder, of a nature compatible with the aggregate and with the operating conditions of the device in which it is placed. This binder completely melts in the flame; it ensures adhesion, cohesion and densification of the product.

 3. an additional compound, which also remains solid during spraying, and reacts immediately during the deposition of the product with the liquid phase resulting from the melting of the binder. This reaction gives rise to the formation of a solid compound at the projection temperature and very refractory.

 In some cases, the additional compound may be the aggregate itself.

 Furthermore, it is possible to add to the material other products reacting in successive phases with the basic products in presence to give new highly refractory solid compounds.

 A series of experiments has shown that it is advantageous to maintain the proportions of binder in a range of 2.5 to 20% by weight of aggregate. Below these values, the adhesion of the product to the wall is compromised by the excessive reduction of the liquid phase formed. Beyond this, the product flows from the wall by creep: there is no longer contact between solid grains, the sprayed layer collapses under its own weight.

 The preferred proportions are in the range 5 let, in particular 7.5% by weight of aggregate, which makes it possible to obtain a layer of sufficient density (3.2) with reasonable energy consumption.

 The proportions of reactive addition product are calculated so that there is complete reaction with the binder and formation of the desired refractory compounds.

 As for the particle size, considerations relating in particular to the optimization of the heat exchanges and to the burner technique, lead to preferring for the main aggregate a range of 10 to 150 micrometers and for the binder a range of 10 to 40 micrometers.

The implementation of the material of the invention is advantageously carried out in a daughter-in-law their multidard of the type described in the French patent application n08215461 in the name of
Applicant. The flame temperature there is of the order of 2200 to 23000C, that of the product which crosses the flame from about 1600 to 1700 C.

 We will now give, by way of nonlimiting examples, compositions of materials in accordance with the invention.

the example
Main aggregate: magnesia
Binder: monocalcium phosphate
Reactive product: lime
Reaction: molten monocalcium phosphate reacts with lime (temperature required for the reaction 13000C) to form tricaloic phosphate (melting temperature 18100C)
2nd example
Main aggregate: magnesia
Binder: monocalcic silicate (wollastonite)
Reactive product: lime
Reaction: the monocalcic silicate reacts with the lime (reaction temperature 15500cl to give silicates diet tricalciques (melting temperatures: 2130 and 21500C)
3rd example
Main and reactive aggregate: alumina
Binder: calcium aluminate (pentacalcium tri-aluminate Ca5A160 4 with a melting temperature of 14550C)
Reaction: the molten aluminate enriches in alumina to form monocalcic aluminate (CaA1204; melting temperature: 16000) then, again by incorporation of alumina, to form penta-aluminatetricalcique (Ca3A110018; o 1720 C)
4th example
Main and reactive aggregate: alumina
Binder: calcium aluminate
Secondary aggregate: MgO magnesia
Reaction: magnesia reacts with alumina to form the spinel MgA1204 (melting temperature 21350C)
5th example
Main and reactive aggregate: alumina
Binder: calcium aluminate
Secondary aggregate: chromium oxide Cr203
Reaction: chromium oxide Cr203 reacts with alumina to form a solid solution A1203 Cr2o3 at solidus temperature between 2045 and 22750C.

 In these last three examples, the temperature required for the reaction is approximately 1500 C.

 In the third and fourth examples, the main aggregate (alumina) reacts simultaneously on the binder and on the secondary aggregate (magnesia or chromium oxide). However, the reaction with the binder (analogous to that of the third example) is very rapid, because it involves a liquid phase, while that with the additive is much slower, because in the solid state. The latter continues, after spraying, as long as the temperature of the sprayed layer remains above 1500 C.

Claims (8)

 1. Hot gunning material for repairing refractory coatings, in particular coatings for metallurgical vessels, material of the type comprising at least two basic products, one of which acts as refractory aggregate and the other as a binder which melts at the spraying temperature of the mixture, characterized in that the material comprises a product capable of entering into reaction at the spraying temperature with at least the binder when the latter is in the molten state to form a more refractory solid compound than the binder.  2. Material according to claim 1, characterized in that the reactive product is an additive distinct from the two basic products.  3. Material according to claim 2, characterized in that the product playing the role of aggregate is magnesia, the product playing the binder roll is chosen from calcium phosphate or calcium silicate, and the reactive product is lime .  4. Material according to claim 1, characterized in that the reactive product is a constituent of the aggregate itself.  5. Material according to claim 4, characterized in that the product acting as an aggregate is alumina and the product acting as a binder is calcium aluminate.  6. Material according to one of claims 4 or 5, characterized in that it comprises an additional basic product playing the roll of secondary aggregate capable of reacting in the solid state at the temperature of the mixture with the first product playing the role of the main aggregate to form a new, highly refractory solid compound.  7. Material according to claims 5 and 6, characterized in that the additional basic product is chosen from magnesia Mgo or chromium oxide Cr203.  8. Material according to any one of the preceding claims, characterized in that the proportions of binder are between 2.5 and 20%, and preferably between 5 and 10%, by weight of aggregate.