DE2011828A1 - Aqueous refractory sizing - Google Patents

Description

PATENT LAWYERS

DR. E. WIEGAND DIPL-ING. W. NIEMANN.

DR. M. KÖHLER DIPL.-ING. C. GERNHARDT 2011 828

MÖNCHEN HAMBURG

TELEPHONE, 55 54 7 « ₈₀₀₀ MUNICH 15.12. ΒΓΖ 1970

TELEGRAMS = KARPATENt · NUSSBAUMSTRASSE 10

W. 14722/70 7 / de

Foseco Trading AG
C hur (Switzerland)

Aqueous refractory sizing

The invention relates to refractory coatings and, more particularly, to coatings for block mold bases and floor panels. Although the sizes can be used outside of this particular area, they will hereinafter referred to in particular as "floor slab finishing".

In recent years, refractory sizes have come into extensive use for application to the base and walls of block molds prior to the pouring of molten metal therein. These coatings serve to protect the base and walls from erosion by the impacting molten metal, to prevent splashes of the molten metal from adhering to the mold walls, and to prevent the cast block from adhering to the mold

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to reduce to a minimum. Have floor slab finishes generally in the form of a suspension of particulate refractory material in a liquid medium. The simple one is brushed, sprayed or otherwise applied to the mold base and walls, and usually dried under the influence of the residual heat in the mold to form a thin, coherent coating.

Floor slab finishes are exposed to very strict conditions in use: the finish must withstand the highly erosive force of molten steel, which ^{strikes from a height of several meters and at a temperature of 1600 0} C or more, the finish must be satisfactory on the floor slab during the entire work process adhere, and the size should also preferably be quick and easy to apply. To date, many attempts have been made to produce floor slab finishes with the desired performance. Most of these sizes are in the form of an aqueous coating composition comprising a particulate refractory material and a binder. It has now been found that particularly good results can be achieved if alkali silicate is used as a binder in combination with a special type of refractory material containing magnesium oxide.

A mass for the protection of floor slabs is known, which consists essentially of a powder mixture of sodium silicate 9HgO and a refractory Filler, such as silicon dioxide, silicon-containing graphite,

1 0 9 8 1 3 MG 7

Kaolin, carborundum, zirconium, chromite or mixtures thereof ". ^{Magnesia calcined at 100 °} C. is also referred to as suitable. The powder is applied directly to the hot bottom plate, and the sodium metasilicate then dissolves in its own water of crystallization, and so does the water then evaporates and gives a dry coating consisting of filler particles bonded by the solid, low melting point sodium silicate It can be seen that such a dried coating can have very considerable compositional variations on a small scale, giving areas of very high content solid sodium silicate and areas with very little or even no sodium silicate content. At steelworks temperatures, such a coating of particles of magnesium oxide with some forsterite (formed by the reaction of magnesium oxide and sodium silicate) would be partially combined with liquid sodium silicate tehen resulting in a coating of moderate strength.

According to a first feature of the invention, an aqueous liquid refractory size is provided, comprising particulate refractory material, which consists of magnesium oxide or encloses this, wherein the teilcheniörnii ~ e refractory 2 ^v Iaterial has a residual hydration capacity of less than 4.Gew .-%, and comprises alkali silicate as a binder. According to a second aspect of the invention there is provided a refractory sizing precursor comprising a mixture of particulate! refractory material consisting of or including magnesium oxide, the refractory material being a residual

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Has a hydration capacity of less than 4% by weight and comprises a solid alkali silicate. Optionally the precursor can be a particulate suspending agent, e.g. Beirtonite included. The amount of in the sizes according to The magnesium oxide present in the invention is preferably sufficient to mix with all of the alkali silicate present to unite.

The particulate refractory material can include, for example, aluminum oxide, titanium oxide, or zirconium (zirconium oxide). The weight ratio of such other particulate refractory material to magnesium oxide is preferably in the range from 4: 1 to 1: 100, especially between about 1: 1 and 1: 4. That is, the magnesium oxide should preferably be at least 20 % by weight of the total refractory present Represent material. The particulate refractory material is preferably a fine quality, for example a material with a particle size of less than 0.075 mm.

The magnesium oxide should preferably have a very low calcium oxide content (in order to minimize the formation of less refractory materials). Preferred Magnesiurnoxyde are dead-burned magnesite, which have been obtained by heating of magnesite to a temperature of at least 1500 ⁰ C. The magnesium oxide used preferably has a residual hydration capacity of less than 3% by weight.

The remaining hydration capacity can be determined as follows: The magnesium oxide is in water during

BAD OHiGlHAL

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Immersed 2 days and then at 110 ⁰ C for 4 hours. Dried. A weighed sample of Mägnesiumoxyd is then heated to 600 ⁰ C for 2 hrs., And it is determined the weight loss. The percent weight loss is the percent remaining hydration capacity.

It has been found that refractory sizes according to the invention provide greatly improved floor slab protection in comparison, for example, with known zirconium-silicate or chromite-silicon dioxide sol coatings or in comparison to the above-mentioned magnesium oxide-sodium metasilicate size.

When sodium silicate is used, reacting the magnesium oxide and sodium silicate in use, and form the highly refractory Silicatforsterit having (in the free state) a melting point of about 1890 ⁰ C (about 200 ° above the highest Stahlgießtemperaturen). An analogous reaction probably occurs with other alkali silicates.

The floor slab coatings according to the invention .can with ferrous metals with a high ferric oxide content with no adverse results or on floor slabs with a coating of iron oxide can be used. The reason for this is probably the very high melting points of solid MgO / FeO solutions that can be formed. Even with a content of 50 wt .- ^ FeO, the melting point is such solid solution only around 1950 ° C (see A.Muan & E.F.Osborne "Phase equilibrium among oxides in steelmaking" published by Addison & Wesley, 1965, page 79).

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The alkali silicate used preferably consists of sodium silicate, in particular sodium metasilicate. The silicate can be used either in the form of an aqueous solution or a dry powder. The floor slab coatings according to the invention can be produced either in liquid form or as a powder, which gives the required coating mass simply by adding the desired amount of water to the powder. The length of water which is present in the liquid size according to the invention must be sufficient to cause hydration of the alkali silicate to at least 10%.

Because of the ease of application of the coatings sprayable compositions are preferred. However, the lower the viscosity, the more refractory it is Material of the coating tends to settle, with a dense cake on the bottom of the container which can be very difficult to redisperse. It is difficult to find suspending agents which work satisfactorily in sizes according to the invention, since the liquid size composition may have a pH as high as 12 according to the invention. However, it has been found that suspending agents Xanthomonas colloids are of particular value.

It is therefore according to a particular embodiment According to the invention, an aqueous liquid size is provided, which is a particulate refractory material, the magnesium oxide includes, and as a binder, alkali silicate

as
and the suspending agent contains a xanthomonas colloid capable of providing a stable suspension under highly alkaline conditions. A particularly preferred

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added colloid is the commercially available "biopolymer X3 23 ". The amount of included in the size Xanchoraonas colloid suspending agent "is preferably 0.01-1.9% by weight. The preferred alkali silicate is Sodium silicate.

In some cases there is a tendency for the size to gel as a result of the reaction between the magnesium oxide and the sodium silicate (dead-burned magnesium oxide reacts in this way). This can be delayed by adding a small amount of a sequestering agent or complexing agent, e.g. Ethylenediamine - tetraacetic acid (EDTA) brings in; usually an amount less than 2 % of such a gown is sufficient.

It has been found that in sizes according to the invention the magnesium oxide preferably contains a few percent iron oxide as an impurity, for example 1 to 6 % thereof.

The invention not only includes the above liquid and solid sizing compositions, but also processes for their application and the by their application received products.

Thus, according to a further feature of the invention is a method for protecting an object against attacks provided at the temperature of molten ferrous metal, at which one can say on the object: "! inenierung

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applied from a refractory sizing as indicated above. The protected item exists usually made of metal, e.g. a block shape or base plate, or devices for handling and treating molten material Metal, but fireproof non-metallic objects, such as fireproof insulated block fο ^ floor panels, can also be used. be protected in this way.

According to a further feature of the invention is an article such as one of those described above Articles, provided, which has a coating of refractory particles, which directly through one another Forsterite are bound. The refractory particles can of magnesia or, optionally, of any of the other particulate refractory materials such as them above, included in sizes according to the invention.

The invention is explained in more detail below with the aid of examples;

example 1

Ss became a size of the following composition

manufactured:

Wt .- ^

tctgeoranges magnesium oxide

(old eiriea content of 4 i "iron oxide) 55 suspension means (Biopolymer XB 23) 0.15 0.7 Ätiiylendiau.intetraessigsäure

liquid sodium silicate (Si0 _?: Na _? 0 ratio 3.3: 1; 37.9 % pesticide; SpecTWew 1.39) 15.0

Water to 100

BATH ORIGINAL

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20 Vl

This size "had an easily sprayable consistency and showed no tendency to rapid Sediinentbildung or to gel formation The sizing was on hot cast iron plates. (300 east; 150 mm χ 150 mm χ 36 min) is sprayed to a thickness of 1 mm, and 200 kg of fully killed steel at a temperature of 1620 ° C were poured onto the coated side of the plate over a period of 100 seconds.

After cooling and testing, it was found that the coating was cohesive and that the panels were not eroded.

Example 2

A liquid coating composition was prepared from the following:

Wt .- ^

dead burned magnesite ($ 100 <0.075mm) 33.75 Aluminum oxide (everything <0.15 mm) 11.25

Sodium silicate (as in Example 1) 12.00 Suspending agent (biopolymer XB 23) 0.15 water 42.85

This size was sprayed onto a heated cast iron plate and allowed to dry. The coating thickness was 2 mm. The cast iron plate was then placed with the coated side up and in one plane arranged at an angle of 45 ° to the horizontal. There was then a stream of molten steel with it a temperature of 1620 ° 0 on the plate from a

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2UMS28

- ίο -

Height of 45 cm at an amount of 2 kg of steel per second poured. The steel had the casting time after 90 seconds Coating not penetrated.

Example 3

It became a liquid coating composition from the following manufactured:

deadburned magnesite ($ 100 <0.075mm) sodium metasilicate 5HpO
(35 gev /.- ^ oige aqueous solution)
Suspending agent (biopolymer XB 23) water

This size was sprayed onto a heated cast iron plate and allowed to dry. The coating thickness was 2 ώή. Thereafter, the cast iron plate was arranged with the coated: side up and in a plane at an angle of 45 ° to the horizontal. A stream of molten steel "at a temperature of 1620 ⁰ G.wurde then to the plate from a height of 45 cm in an amount of 2 kg of steel per second poured. After 90 see, the plate was cooled, and it was the exposed surface The surface of the crystal structure was analyzed to determine the relative proportions of the various refractory components present in the particular observation plane. The following results were then obtained:

45 75 22 15th O, 1 32,

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2ÜVI828

area

The results were

(# -Face of the photomicrograph):

Periclase (MgO) 35

Forsterite 50 spinels, glasses and others

Silicates 15

An X-ray diffraction analysis of an amount of the powdered coating residue indicated a total forest grade content, based on the total coating density, of 6 to 8 $.

Example 4

A dry powder mixture of the following composition was prepared:

Wt .- ^

Magnesite (£ 100 <0.075mm) * 77.5 Natriuiametaailicat 51 ^, 0 (powder) Suspending agent (powdered bentonite clay) 3 »5

To produce a floor slab coating that is suitable for use in the usual manner, e.g. by spraying, it is necessary to use the above-mentioned composition to be diluted in any convenient ratio between 60:40 and 40:60 (by weight).

Line special sizing, which had been made with water in a ratio of 50:50, was how

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20 Vi

in Example 2 "described, tested. After a pouring time from 90 seconds the steel had not penetrated the coating.

For comparison purposes, 2 refractory coatings were made as follows:

Comparative example 5

A dry powder mix was made the end:

Weight %

Magnesium oxide (caloinated at 100 ° C) 60 liatrium metasilicate 9HpO 40

150 g of the powdery mixture were applied to a hot test plate (300 ° G), after which the Crystallization water was driven off and a hard mm thick solid coating remained on the plate.

Comparative example 6

A liquid size of the following composition was produced, "'--'-' ^ - ~ -t:

Weight -j *

Olivinsaud (91 i> Poraterite) 50

liquid sodium silicate (38 %

Pesticide; SiO ₉ : Na ₉ O ratio

3.3: D ^Δ 13.5

Suspending agent (biopolymer XB 23) 0.15

Water 36.35

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The size was sprayed onto the hot test panels, with a dry coating in one Thickness of 2 mm.

These sizes were tested according to the methods used in Examples 2 to 4. the Coatings failed, i.e. erosion of the test cast iron plates began at 16 seconds (Comparative Example 5) and at 14 seconds (comparative example 6).

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Claims (15)

Claims 1. Aqueous liquid refractory sizing that is particulate refractory material consisting of or including magnesium oxide and alkali silicate as a binder, in particular sodium metasilicate, characterized in that the particulate refractory Material has a residual hydration capacity of less than 4% by weight. 2. Refractory sizing according to claim 1, characterized in that an amount of water is present in the sizing which is sufficient to cause hydration of the alkali silicate to at least 10 H ₂ O. 3. Refractory size according to claim 1 or 2, characterized in that it contains a suspending agent, for example a xanthomonas colloid, in an amount of 0.01-1.9% by weight of the size. 4. Refractory size according to one of the claims 1 to J3, characterized in that they contain up to 2% by weight of a metal ion sequestrant. 5. Refractory size precursor which is a mixture of particulate refractory material, which consists of or includes magnesium oxide and a solid alkali silicate, preferably sodium metasilicate, characterized in that the refractory material has a residual hydration capacity of less than has 4 wt. 109813/1020 6. precursor for refractory sizing according to claim 5, characterized in that it is a particulate suspending agent, e.g. bentonite, 7. Refractory size or precursor therefor according to any one of claims 1 to 6, characterized in that the magnesium oxide has a residual hydration capacity of less than 3% by weight > has. 8. Refractory size or precursor therefor according to any one of claims 1 to 7, characterized in that the ca ^ nesiuinoxide is obtained by heating magnesite at a temperature of at least 1500. ⁰ G. 9. Refractory size or precursor therefor according to one of claims 1 to 8, characterized in that that the Kagnesiunoxyd as an impurity 1 to 6 wt .-? 6 Contains egg s enoxide. 10.! Refractory sizing or precursors for it according to one of claims 1 to 9, characterized in that that the partially uniform refractory material is all has a particle size of less than 0.075 mm. 11. EeüGrfeate finish or forerunner for it according to one: of claims 1 to 10, characterized by gekenjiz-eichnet, that at least 20 percent by weight of the particulate refractory Materials consist of magnesium oxide. 12. Refractory sizing or precursor therefor according to one of claims 1 ois 11, characterized in that the refractory material includes aluminum oxy, titanium dioxide or zirconium. 10981 3/1020 BAD ORiGlNM. 13. Refractory size or precursor therefor according to one of claims 1 to 12, characterized in that that the amount of magnesia present is sufficient to mix with all of the alkali silicate present to unite. 14. Aqueous liquid refractory sizing which is a particulate refractory material, magnesium oxide includes, and comprises alkali silicate, in particular üfatriumailicat, as a binder, characterized in that that it contains a xanthomonas colloid as a suspending agent, which is capable of forming a stable suspension to deliver strongly alkaline conditions. 15. Object with a coating of refractory Particles, e.g. 3. particles made of magnesium oxide, aluminum oxide, titanium dioxide or zirconium, characterized in that the particles are directly connected to one another by forsterite.