DE2414808A1 - MONOLITHIC FIREPROOF BODY - Google Patents

Description

concerning:
Mono lithisch he refractory body r

The invention relates to monolithic polycrystalline sintered bodies on the basis of alumina for lining shaft furnaces, crucibles or nozzles for receiving metal melts and the like. and contains 15 to 50% by weight of silicon arbiakora dispersed in egg clay, preferably in a grain size between about 3.36 and 0.35 mm. However, in the Qedeia case, at least 75 % should be coarser than 0.149 mm. Such bodies are characterized by outstanding thermal stability and resistance to temperature changes

Sintered clay bodies are excellent refractory linings for furnaces, but tend to crack or split with rapid temperature changes. The invention relates to new sintered alumina bodies of improved temperature week resistance by incorporating coarse silicon carbide particles into the bodies.

From the 'US-PS 2,770,552 a silicon carbide is content of

409842/0798

1A-44 676 - 2 -

17 »5 to 25 % known in clay. These bodies v / ground fired at at least 1650 ⁰ C. They should have better heat resistance and compressive strength than silicon carbide or tors earth. Because of the relatively coarse alumina, relatively high firing temperatures are required for the appropriate strength. Dolch's firing temperatures convert part of the SiliciiMicarbids to silicic acid, which in turn reacts with clay to form hullite, so that the bodies stick together. Furthermore, the use of 50 to 70 % silicon carbide in an aluminum silicate system is known.

The invention now relates to a body with a low modulus of elasticity and higher resistance to temperature changes than was the case with known products, namely completely self-bonded alumina structures containing coarse grains of silicon carbide the firing temperature is low enough to avoid the formation of silicate due to the oxidation of silicon carbide. Appropriate; Strength is achieved at such low firing temperatures by distributing coarse silicon carbide grains into the fine active alumina and sintering to the required strength at temperatures below 1535 ° C. The products obtained have a modulus of elasticity of about one third of the equivalent-sintered alumina body and do not suffer any reduction in strength when heated to temperatures of about 1250 C, in addition they have higher V / ärmeleitfähigkeit and thermal shock resistance than conventional products _t the silicon carbide alumina contained.

- 3 409842/0798

676 ² < ^U808

Preferred approaches i-Ür plates or saggers in ovens are the following:

Silicon Carbide - 0.72 to 2 mm (10-24 mesh) 35 % Tabular Alumina - ^ 0.59 mm (-28 mesh) 22 # Tabular Alumina - «* Ο, 147 ram (-100 mesh) 20? Ί Tabular Alumina - - 43 #um (-325 mesh) 8 # Reactive clay

(mean grain size 2.5 / um) 15> '-

Dextrin 1 part / l 00 parts

Dry mix

Mixing water 3 parts / 100 parts

Trockengeniis ch

The tabular clay is commercially available Products obtained by firing Bayer Alumina. It 5.st essentially ^ - clay very high purity.

An essential component of the above mixture, which must be present in an amount between 10 and 40 $ 5 of the C-esaratgo content, is reactive clay, which is a high-purity oil clay with a mean grain size of "^ 4 Am"

The above mixture is filled in a corresponding mold pressed _t (3 t / sq.in), dried at 82 ° C and at 145 ° ° C fired "is A corresponding Erennprogramm a Aufheisgeschwindigkeit of about> 7fiß ^o c / h up to 1450 ⁰ C. and baking for 4 hours at this temperature, followed by cooling in the oven in 10 hours. Instead of pressing, you can also use slurry.

409847 / 079B

1A-44 6/6 - 4 -

In addition to furnace lining or furnace inserts, the -rli ^ ciungEgeiBäß also suitable as crucibles or r.-ü .-. T.nstc.iyx · cdcir other formulas, the considerable temperature; 'n.oerungen au / ige sets are.

lh: * ^f , ~ c ho π 'ion oMrc-n "preferred approach and manufacturing process, different variations are possible. In any case, the silicon carbide portion should be between 15 and

'/> α er can mourn Πο ^ .-, ί, whereby at least 7 ¹ J Toi ⁷ - coarser than GyI ·; 0: λιϊϊ r; oin should. Preferred liogt «rg Siliciu ^ oa ^ ic! between 0.35 and 3, ^ 56 mm in front (6 to 46 mesh USSS).

Dia preferably applied to high purity alumina baritiirn and not fortified eic 4: - 'Kieselsäuro, 0.1 ^ Ilatriuiso'iid, 0.5 r> Bisenörcid (Fe ₀ O ₇₎ and not more ds total of 0.5 i? Ro (CaO ₁ HgO, l '& iö) E * can, however, replace inert oxides of molten or pintered zirconia or Al'uminiu.r.2.iikoiiat up to 235e of the alumina. Ta the coir; In this case, the limit values for silicon carbide would have to be re-established and 2was based on volume, ie products which only contain alumina (in addition to silicon carbide, of course).

The grain size of the clay is important insofar as there is sufficient active clay to achieve a corresponding strength at maximum firing temperatures of 1450 to 1535 ° C. This makes it necessary that the entire dry matter contains 10 to h0% ΤοΓ .srde with a grain size of -4 / µm.

4098Δ? / 079 «

The normal soil should be different grain fractions auxvio.icuin, in order to achieve the appropriate density in the finished product (up to gri t; A)

The obstruction-compliant objects have a slastisits.tsifiodul of 27 »10 dynes / cm compared to sintered toners Ae) with a modulus of elasticity of 75 bin 100 · 10 ^1½ . Of the

Bruchmoaul is at room temperature boi £ 4 and at 1'150 ^w boi 150 kg / cm ² (1200 resp.

Esi the preferred eriindiiBgsgGKäSon body korai / il "es with the Brermer) su eirtesi gev / issen Kormvachötur, -; dor, /■■j.vnii.rJx oxids. So there is shown in the Ferl'-igprad'akt-j Cad for Optiiaale results the clay in a size --10 / ^un in an amount of at least 8 Ge \ r * ~% and --.- 50 yim in an amount of at least 25 Gov / "->i" oll,

Bio he dispute of the Sintertouerdo is umgokeivrt proportional their grain size. So it's wishing / sv / for . firmer Gcgonctände fine kriatalline! Eonerdo ^ iiabe-a; although the Tonerdabindim ^ primarily Mb3r fine recrystallized alumina is done so is the inventive product is relatively v / itself and ne a low modulus of elasticity «VfUhronä die Alu g is solid, the product contains two PJ'-

(Aluminum oxide and silicon carbide) laiti ^ -r different thermal expansion coefficients, namely 9 x 10 ^^ hz \ -:, k _f 5 x 10 "6 / grd _e Such differences must lead to tensions and cracks in the structure of the body. This again ! explains the low i lastiz, itutcnodui Lind * rkcitsv- the Feßti; erte other hand ißfc this combination gi-rade ^d ^ '_ high thermal conductivity, the low modulus of elasticity and the strained structure.

- 6 409842/0798

ORIGINAL INSPECTED

24H808

1A-44 676

Polygamy i-.u bo .-- crer Tc-mo lu: ': s.:iiLt^:i jCUrnor leads. So vr-'rde boinpielsv / oise ciiiü Soheiba with a diameter of 152 mm hinriclitlj.ch. ¹ Ci ^ TGuipüraturv / self-reliance compared iT.il; Hand-oiled clay, mullite and silicon carbide disks are heated in an oven to 1200 ° C, in the air until they break, are cracked, cut off, dried, etc. Only the inventive product held 10 vocabulary ϊ-us.

The manufacture of the bodies according to the invention is done by mixing the starting materials, drying, drying the in ^ s and burning at 1300 and 1535 ⁰ C,

ORIGINAL INSPECTED

4098Λ7 / 079 0

Claims (4)

SUBMITTED 2AH808 1-44 676 r ir ft Xt t «.η r> ryv ü c he 1 »T'onolithiso'j ^ r refractory object» "bcctuhend Iia WcSentliehen r: u3 ^ ofcuadejion particles of alumina w: 0 crystals «05 to i? 0 Gev; .-? 5 aluminum oxide crystals, 0 Mv 20 Csvr.-J: 'zirconium oxide, where"suaind'.u't25?' der /:Xv.Min5.\rv· cxidkristcllo finer than 50 /U.-·, ■ suaiiiceöt S; ', us.r Alv: - iniv-.i-oxitlkrictalle faincr than 10 / Utu and?; v'3 at least 73 Γ- deP silicon carbide crystal ^ are coarser than 0.14? ^ M * 2. Product according to claim 1 »dechn-eh β e ks nn- E eich η G t that the piliciusucarbitic crystals ei: ae l'cirmmg svi-ische.n. 0.35 and 3 »36 vm bositaen. 3. Product according to claim 2 or 3, characterized GEK e η η is characterized in that the alumina - 0.1 ~ - J ^ ₂ ^ o _r --- 4 sloj ,, -.? R = 0.5 5 Fe ₂ O ^ and - * z 0.5? I PlO contains. 4. Product according to claim 1 to 3, characterized in that g e k e η η that the modulus of elasticity ^ 35 s 10 dyn / cii 'and the transverse flexural strength at least 70 kg / cm amounts to· 5 · Product according to claim 1 to 4, characterized in that geke η. η shows that 10 to 40 # reactive oC-alumina with an average grain size of ^ - 4 / µm is present in offset v / ar · .. ORlGtNAL INSPECTED