DE2321810A1 - FIRE-RESISTANT FIRED SHAPED BODIES AND METHOD OF MANUFACTURING THEREOF - Google Patents

Description

VXE / P / Dr.Se / Fk Case 2628

P I D I E R - W E R K E A G 62 Wiesbaden, Lessingstr. 16

Fireproof molded articles and processes for their manufacture

The invention relates to refractory fired molded articles for Closures on casting units for steel, iron and metal (Nozzles, plugs, spouts, slides) on the basis of Zirconium oxide and zirconium silicate and a process for their production. ■

When casting from Gießaggregaten, for example of liquid steel from pans "refractory seals are used. These closures sit in or on the casting unit. The task of these refractory closures is to keep the amount of steel flowing out through them as constant as possible in the unit of time in order to optimize the subsequent solidification and cooling process. The amount of steel escaping per unit of time is essentially dependent on the height of the steel bath in the casting unit and the Locliqu he cut of the closure.

The closures are therefore subject to high requirements in terms of wear resistance compared to high temperatures flowing steel, iron or metal, in addition, in terms of insensitivity to abrupt changes in temperature, since the casting units used with the specified Closures are provided, spontaneously with highly heated,

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molten material (steel, iron and metal). Because of these high loads, one already has Zirconium silicate (ZrSiO.) As a material for production used by closure parts, e.g. nozzles. However, those are There are limits to the possible uses of zirconium silicate nozzles. Difficulties arise with zirconium silicate nozzles at Irangen casting times and when casting unskilled or alloyed steels. The heavy use expresses itself in a noticeable widening of the nozzle hole cross-sections, which results in an uncontrolled change in the casting speed. With the transition to closures from zirconium oxide or dense aluminum oxide, attempts have been made to To remedy the situation. Wide application of such products In addition to a very high material price compared to zirconium-silica products, they are above all one high thermal shock sensitivity of such products.

Attempts are also known to use mixtures of zirconium oxide with zirconium silicate as a starting material for refractory bricks. In their book "Feuerfestkunde", 1960, Springer-Verlag, p. 906/7, for example, Harders-Kienow propose a mixture of 1000 g of zirconium oxide with 500 g of zirconium silicate (66.66 wt. 56 ZrO ₂ and 33, 34% by weight ZrSiO.). The stone produced is only used for insulation purposes. Its use as a molded body for closures on casting units for the transfer of molten steel is prohibited because of its high porosity. On the contrary, a molded article for casting purposes must be dense in order to effectively resist corrosion.

The invention is based on the object for installation in closures on casting units for steel, iron and metal

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affordable quality based on zirconium material for moldings that combine the advantages of high wear resistance with high insensitivity to thermal shock.

The object is achieved in that the proportion of zirconium oxide is 10-50% by weight , preferably 35% by weight, the proportion of zirconium silicate 50-90% by weight, preferably 65% by weight, and that the zirconium oxide in one Distribution of 30 - 60% by weight of the total amount of zirconium oxide in stabilized form and 70 - 40% by weight in non-stabilized form. The zirconium oxide is introduced in a grain size of at most 0.1 mm, preferably smaller than 0.06 mm, the zirconium silicate in a grain size of over 0.2 mm, preferably 0.2-0.5 mm.

The idea is to measure the proportion of zirconium oxide (grain size below 0.1 mm, preferably smaller than 0.06 mm) based on introducing this valuable material only in such an amount as is necessary for good corrosion resistance necessary is. This corrosion-resistant material forms in the finished stone because of its fine grain the matrix, which in general is particularly susceptible to slagging. ·

By using cheap zirconium silicate in an amount of 50-90% by weight, preferably 65% by weight of the mixture, is a price advantage over materials with the same Durability guaranteed. Through its use in the coarser Grain (0.2 - 0.5. Mm), the slag strength is this is more closely aligned with the latter due to slagging.

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The composition according to the invention - in the coarse grain zirconium silicate, in the fine powder zirconium oxide - results as the structure of the fired body in a framework made of zirconium silicate with an intervening matrix of sintered zirconium oxide. Because the well-known dissociation of ZrSiO ₄ at high temperatures

ZrSiO ₄ - * ZrO ₂ + SiO ₂

starting from the inner surface "in the composition of the mixture according to the invention (ZrSiO ₄ = coarser grain) the proportion of the silica released by decomposition is many times less than it _{corresponds to the quantitative substitution of ZrSiO 4} in the mixture by ZrO". This in turn has the consequence that the matrix contains fewer low-melting compounds and is therefore much less effective against corrosion attack at high temperatures. On the other hand, the framework made of ZrSiO ₄ gives the fired product good thermal shock resistance.

The zirconium oxide to be added according to the invention is a material the volume changes reversible in its original modification at elevated temperature (over 1000 C) which leads to vibrations within the structure of masses that contain this material in excess. This one One avoids the disadvantage if one uses stabilized zirconium oxide. In order to introduce fluxes into the Zir- Konoxidmatrix beyond a certain level and one from it to avoid the resulting risk to your fatigue strength, the addition of stabilized zirconium oxide, which is known to contain CaO as a stabilizer, is limited in terms of quantity.

The upper limit of the addition is 60% by weight of the total Zirconia material. On the other hand, a minimum addition is necessary, to achieve the stabilizing effect in the mixture

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hold (minimum addition 30 wt. # of the amount of zirconium oxide).

The moldings are produced both in ceramic Slip casting as well as in the pressing process. To avoid contamination of the starting material, the Casting process a slip containing zirconia. Either this is used as the binding agent in the pressing process Slurry or organic binding agents «The slurry is used to prevent contamination of the zirconium material by abrasion. to avoid foreign matter, manufactured in a wet mill, the lining of which consists of zirconium oxide moldings, which are in suitable shaping also act as grinding media.

The invention is explained using the following exemplary embodiments.

a) Slurry pouring process

83 kg stabilized zirconium oxide »grain size below 0.1 mm, and 83 kg of non-stabilized zirconium oxide, grain size less than 0.1 mm, are mixed with 34 liters of water and 5 milliliters

- '■■ aqueous solution of an alkali salt of a polycarbonate '3 acid in a wet mill loaded with zirconium oxide grinding media, those with a lining made of shaped zirconium oxide stones is provided, milled for 200 hours. After this time, 40 parts by weight of this slip are added and 60 parts by weight of zirconium silicate, grain size 0.2-0.5 mm mixed in. This mixture is poured into plaster molds, after 12 pounds

burned.

switched off after 12 hours, dried and at 1620 ° C

b) pressing process

650 kg of zirconium silicate, grain size 0.2 - 0.5 mm, are ■ mixed in an egg mixer with the addition of 15 liters Sulphite waste liquor (30 ° B) with 175 kg stabilized zirconium oxide * smaller than 0.06 mm, and 175 kg non-stabilized zirconium oxide approx. 10 minutes

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mixed. The finished mass is pressed in a hydraulic press under a pressure of 500 kg / cm. The compact is dried and then fired at 1620 ⁰ C.

Nozzles for casting steel produced by this method have the following property values

Chemical Analysis;

ZrO ₂ 1 75 Weight % CaO »5 Weight % SiO 20th Weight %

Physical properties: bulk density 4.0 g / cm

Specific weight 5.0 g / cm ^J

Porosity, total 20 vol

Nozzles according to the invention have proven useful in steel mills well proven.

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Claims (7)

1. Fireproof, fired molded body for closures on casting units for steel, iron and metal (nozzles, stoppers, spouts, slides) based on zirconium oxide and zirconium silicate, characterized in that the proportion of zirconium oxide is 10-50 wt. #, Preferably 35 wt ...%, the proportion of zirconium silicate 50-90 wt%, preferably 65 wt%, and that the zirconium oxide in a pitch of 30 -. 60% Gevr the total amount of zirconium oxide in stabilized form und'70 -. 40% by weight in not in a stabilized form. 2. Refractory fired molded body according to claim 1, characterized in that the zirconium oxide in grain sizes less than 0.1 mm, preferably less than 0.06 mm, is introduced. 3. Refractory fired molded body according to claims 1 and 2, characterized in that the zirconium silicate in a grain size over 0.2 mm, preferably 0.2-0.5 mm, is introduced. 4. A method for producing a refractory, fired molded body according to claims 1 - 3, characterized in that that the shaping in the ceramic slip casting process takes place using a zirconium oxide-containing slip. 5. The method according to claim 4, characterized in that the production of the zirconium oxide slip required for casting in a wet mill, which is lined with zirconium oxide moldings, with the help of zirconium oxide ■ "jtial bodies is done. '" 409846/057 8 6. The method according to claim 1-3 »characterized in that the shaping of the stone takes place in the pressing process, zirconium dioxide slip or an organic binder being added as a binder to the mass. 7. The method according to claim 1-6, characterized in that the deformed body after drying at temperatures is fired over 1600 ° C. 409846/0578