DD274207A1 - SINTER MULLITSCHAMOTHOUSES WITH GOOD THERMAL ROOM RESISTANCE - Google Patents

Abstract

The present invention relates to sintered mullite chamotte bricks with good thermal stability, which are used for the delivery of pyrotechnic systems with a Formsteinausmauerung, primarily of glass tubs. According to the invention, a mixture of sintered mullet clay defined in the grain size and binder clay with a high proportion of free quartz and / or refractory binding clay and / or kaolin and / or a mixture of ground alumina and refractory kaolin and quartz flour and fine-grained noble and / or normal corundum to achieve the thermal stability of silicon carbide and / or silicon and / or zirconium silicate all with a particle size kl. 2 mm, preferably kl. 0.5 mm, this mixture is compressed by the dry pressing process into moldings and sintered at temperatures of more than PK 140, preferably around PK 150. The silicon carbide or silicon or zirconium silicate is only insignificantly converted to SiO 2 during the erosion of rocks. It is only when using the stones in pyrotechnic systems that SiO.sub.2 is gradually formed, which reacts with the excess corundum present in the sintered mullite to form mullite, whereby the shrinkage of the sintered mullite stone caused by a bulk crystallization of the mullite is compensated and the stone thus becomes thermally stable.

Description

Field of application of the invention

This invention relates to sintered mullite chamotte bricks having good thermal space stability for the delivery of pyrotechnic systems having a stone lining, primarily glass trays.

Characterization of the known technical solutions

Known from the specialist literature are mullite stones based on highly sintered mullite, with kaolin and / or a kaolin-clay mixture being used as binder. The corresponding Sintermullitkörnungen (grain fractions 1 to 3 mm, less than 1 mm, less than 0.2 mm) are mixed with the binder and pressed by the dry pressing on hydraulic or screw presses and the moldings then sintered at PK 171 to 175 in the tunnel furnace. These materials are mainly used in glass tubs. At high temperature loads such as in heat-insulated glass tubs, where the heat can not be dissipated to the outside, these materials are subject to irreversible Nachschwindung, which can lead to premature failure of the glass tubs by collapse of the lining. The cause of the shrinkage is a collective crystallization of the mullite, in which the surface energy is reduced by the transformation of the many mullite crystals into large crystals to reach the lowest energy state. It is also known from the literature the addition of white corundum to sintered mullite stones to improve the pressure endurance behavior. Despite the improved pressure endurance, there is also some afterglow in this variant, but this is reduced compared to the pure sintered mullite variant. Also known is the production of sintered mullite stones in which mullite is produced in the bond by adding quartz powder and fine corundum. The Nachschwind at high temperatures is indeed limited in these stones when SiO _{2 is introduced} in such an excess that after the sintering of the stone material still free SiO _{2 is} present.

However, the reaction during the erosion of rocks is not controllable so that the stone material has satisfactory Gefüggewerte. The SiO ₂ , which is not required for binding, reacts with the free corundum present in the mullite amoeba, but due to the formation of the mullite and the associated density reduction, the material grows even at temperatures of around PK 150 during the erosion of rocks, so that the open porosity is not below 20 % can be kept.

In addition, it is known that predominantly stones are used on SzwmelzmuHitbssis in highly stressed glass tubs. Since the enamel mullite has very large mullite crystals, there is no accumulation crystallization even at high temperatures, and thus enamel mullite stones are constant in constant flow under temperature stress. However, a disadvantage is the high energy required to produce the Schmelzmullits.

Object of the invention

The aim of the invention are sintered mullite stones with good thermal stability, whose open porosity are below 20% and which, when used in pyrotechnic systems, primarily in glass tubs, are subjected to no winding, whereby the service life of the refractory lining can be extended.

-2- 27 * 207

Explanation of the essence of the invention

Task wt.r it to develop sintered mullite stones, which have no irreversible shrinkage at use temperature. Erfindungsgemäl. '. is a mixture of defined in the grain size Sintermullitschamotte and binding clay with a hv-hen share of free cuarz and / or refractory binding clay and / or kaolin and / or a mixture of ground alumina and refractory kaolin and quartz powder and fine-grained noble and / or Normal corundum for achieving the thermal stability of silicon carbide and / or silicon and / or zirconium silicate, all with a particle size kl. 2mm, preferably kl. 0.5 mm and this mixture is molded on the dry pressing on hydraulic or screw presses. After drying, the stones are sintered at more than PK 140, preferably around PK 150. The SiC or Si or the ZrSiC> 4 is converted during the sintering of the stones only to a small extent to SiO ₂ , the predominant part is in the original form.

Therefore, the sintered stones have values of the open porosity below 20%, by adding small amounts of SiO ₂ or using a binding clay with a high content of fine crystalline free SiO ₂ very good cold compressive strengths can be obtained. It is only when the stones are used in the pyrotechnic system that SiO ₂ is gradually released, which replicates with the surplus corundum and mullite present in the sintered mullite. This compensates for the shrinkage caused by the bulk crystallization of the mullite, and the stone material is space-stable. At temperatures above 1500 ° C, there is even a small volume expansion and thus the bracing of the refractory lining.

Embodiment 1

In a mixing unit, preferably counterflow fast mixer

45% Sintermullitschamotte, Kornfraktion 1-2,5mm

31% Sintermullitschamotte, Kornfraktion 0-1 mm 5% Edelkorund EK 0OWS after TGL 8783 and 2% silicon carbide, grain mix 0 / 0.3 to TGL 8005/01

added dry pre-mixed and then mixed with 2% sulfite liquor to improve the green strength of the fresh Prsßlinge and 0.3% water. Thereafter, 5% of binder clay with high levels of active quartz and 12% Sintermullitschamotte, grain fraction kl. 0.1 mm mixed. The ready mixed mass is transferred to the hydraulic or screw presses and processed there with a specific molding pressure of at least 5OMPa ζ appropriate Formsieinen.

The bricks are dried and then fired at temperatures around PK 150. The resulting stone quality is characterized by the following values:

Al ₂ O ₃ and TiO ₂ content 69.3% density 2.48 g / cm ³ Open porosity 17.4% Cold crushing strength 64.3 MPa Pressure Fire Resistance Ta gr.1700 ° C

The irreversible linear change in length after 20 burnup at a cone drop point of the PK 173 (corresponds to about 400h at 1700 ⁰ C) is + 0.2%, with a Sintermullitsteinqualität conventional production, the value of the same firing conditions is -1.4%.

Embodiment 2

In a mixing unit, preferably counterflow fast mixer

45% Sintermullichamotte, grain fraction 1 ~ 2,5mm

28% Sintormulli chamotte, grain fraction 0-1 mm 5% precious corundum EK 0OWS according to TGL 8783 and 2.5% silicon carbide, grain mix 0 / 0.3 according to TGL 8005/01

added, mixed and treated with 2% sulfite liquor and 0.3% water. Thereafter, 7% of the raw mixture for Sintermullitherstellung, consisting of 50% ground alumina and 50% milled kaolin Caminau and 12.5% Sintermullitschamotte, grain fraction kl. 0.1mm mixed. The molding and the burning done as in the embodiment 1

 The stone quality has the following quality values:

Al ₂ O ₃ and TiO ₂ content 69.7% density 2.48 g / cm ³ Open porosity 18.2 g Cold crushing strength 55,6MPa Pressure Fire Resistance Ta gr. 1700 ⁰ C

The irreversible linear change in length after 10 burnup at a cone drop point of the PK 173 is + 0.3%, as opposed to -1.1% for a sintered mullite brick quality of conventional production.

Embodiment 3

As in embodiment 1 were

50% Sintermullitschamotte, Kornfraktion 1-2,5mm 32,5% Sintermullitschamotto, grain fraction 0-1 mm 5% corundum, EK 0OWS after TGL 8783 2, b% silicon carbide, Kömunqsgemisch 0 / 0.3 after TGL 80US / 01 3% quartz flour , Fineness W8 and 7% raw mixture for sintered mullite production with sulphite waste liquor and water gbruischt, molded and fired, stone type has the following quality characteristics:

Al ₂ O ₃ and TiO ₂ content 69.0% density 2.45 g / cm ³ Open porosity 18.7% Cold crushing strength 89,6MPa Pressure Fire Resistance Ta gr.1700T

The irreversible linear change in length after 10 burnups at PK 173 is + 0.2%

Embodiment 4

As in embodiment 1 were

45.0% Sintermullichamotte, Kornfraktion 1-2,5mm 12,5% aintermullichamotte, Kornfraktion kl. 0.1 mm 30.0% Sintermullitschamotte, grain fraction 0-1 mm 5.0% Edelkorund SK 0OWS according to TGL 8783

2.5% silicon carbide ground to a grain fraction with a screen residue on the 0.063 mm screen of 31% 5.0% binder clay mixed with a high proportion of fine quartz with sulfite liquor and water, molded and fired. The stone quality has the following quality values:

Al ₂ O ₃ and TiO ₂ content 69.2% density 2.49 g / cm ³ Open porosity 15.5% Cold crushing strength 92,9MPa Pressure fire resistance T _A gr.1700 ° C

The irreversible linear change in length after 20 burnup at PK 173 is + 0.1%

Embodiment 5

As in embodiment 1 were

45% Sintermullitschamotte, Kornfraktion 1-2,5mm 30% Sintermullitschamotte, Kornfraktion 0-1 mm 10% ErJelkoruryJ EK 0OWS after TGL 8783 5% Bindeton with a high portion of free quartz and

10% silicon carbide, mixture 0 / 0.3 according to TGL 8005/01 mixed with sulphite liquor and water, molded and fired. The stone quality has the following quality values:

Al ₂ O ₃ and TiO ₂ content 63.4% density 2.47% Open porosity 18.0% Kdltdruckfestigkeit 82.8% Pressure Fire Resistance Ta gr.1700 ° C

The irreversible change in length after 10 burnings at PK 173 is + 0.15%.

Embodiment 6

As in embodiment 1 were

45% Sintermullitschamotte, Kornfraktion 1-2,5mm 30% Sintermullitschamotte, Kornfraktion 0-1 mm 13% Sintermullitschamotte, Kornfraktion kl. 0.1 mm 5% precious corundum EK 0OWS according to TGL 8783 5% binding clay with a high content of free quartz and

2% FeSi 95 according to TGL 6782 (Fe content by 0.5%, sieve residue on the 0.04 mm sieve by 88%) mixed with sulphite, jug and water, molded and fired.

The stone quality has the following quality values:

Al ₂ O ₃ and TiO ₂ content 70.1% density 2.42 g / cm ³ Open porosity 19.7% Cold crushing strength 37.8% Pressure Fire Resistance Ta gr. 1700 ⁰ C

The irreversible linear change in length after 10 burnings at PK 173 is ± 0%.

Embodiment 7

As in embodiment 1 were

45% Sintermullitscf'dmotte, Kornfraktion 1-2,5mm 30% SintermullitschamoUe, Kornfraktbn 0-1 mm 5% Sintermu'litschamotte, Kornfraktion kl. 0,1 mm 5% Edelkon nd EK 0OWS acc. To TGL 0783 5% Bindetor · with a high content of free quartz and 10% zirconium silicate (sieve residue on the 0,04-mm sieve around 14%) mixed with sulphite waste liquor and water, molded and burned. The stone quality has the following quality values:

A ¹ Aa and TiO _r content 61.9% ZrO _r content 6.6% density 2.48% Open porosity 19.8% Cold crushing strength 39,2MPa Pressure Fire Resistance T gr.1700 ° C

The irreversible linear length change after lOmügembrenner at PK 173 is + 0.05%.

Claims (2)

Sintormullichamottesteine with good thermal stability, consisting of 62-90% Sintermi ^: chamotte and 0-10% binding gate _(with a high level of free quartz and / or 0-15% refractory binding clay and / or kaolin and / or a mixture of ground Alumina and refractory kaolin
as well as 0-3% quartz flour and 0-10% fine-grained noble and / or normal corundum characterized in that the masses to be pressed to formations to achieve the thermal stability 2 to 10% silicon carbide
and / or 2 to 10% silicon
and / or 5 to 15% zirconium silicate, everything with a grain size kl. 2 mm, preferably kl. 0.5 mm added and the moldings are sintered at temperatures greater than PK 140, preferably around PK 150.