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22 TECHNICAL PAPER


PATCH SLA 1


Component SLA-92


Cement Additives


H2 O Castable properties Bulk density


thermal conductivity (prefired 1000°C/5h)


110°C / 24h 1000°C / 5h 1500°C / 5h 20°C


300°C 600°C


1000°C 1200°C


Table 3: Patch mix formulations based on SLA-92


PATCH SLA 2 is lower and the formulation contains a higher amount of cement CA-270 and reactive alumina CL 370. An addition of clay here is not required. CMC is added in both mixes to improve the stickiness and plastic consistency. PATCH SLA 2 provides a good deal of flexibility with regard to the castable composition. The SLA-92 content can be increased up to 80% and consequently the content of CL 370 and CA-270 can be decreased. The consistency of both mixes can be adjusted in a wide range by varying the water addition, and can therefore be adjusted to specific requirements of the application.


Results and Discussion


The chemical compositions of the test castables are listed in table 4. All castables show a constant composition of about 89% Al2


O3 O3 below 0.1% and SiO2 below 0.5%. and 10% CaO


independent of which aggregate is used. The impurity level for all mixes is very low: Fe2


The fired density of the different vibration castables was adjusted within the range from 1.1 to 2.7 g/cm³ (figure 3). The higher the density, the higher the Bonite content in the mix and the lower the SLA-92 content. A castable formulation representing the density range of 1.8 – 2.0 g/ cm³ was excluded from the investigation due to the segregation. This formulation required coarse SLA-92 in combination with different Bonite sizes and the coarse SLA-92 tended to segregate.


The strength properties shown in figure 4 and 5 correlate with the fired densities. When comparing the pure SLA-92 containing castables VIB 1.1 and VIB 1.3, the cold modulus of rupture is improved by a factor of two and the cold crushing strength by almost a factor of three for VIB 1.3. This is due to the matrix optimisation by using tabular alumina fines, calcined and reactive alumina and dispersing aluminas as additives. The


VIB 1.1


Chemical composition Al2


O3 % 88


CaO % 11 Fe2O3 SiO2


% < 0.1 % < 0.1


Table 4: Chemical composition of CA6


VIB 1.3


89 11


< 0.1 < 0.1


based castables


VIB 2.2


90 9


< 0.1 0.3


VIB 2.4


90 9


< 0.1 0.3


VIB 2.6


91 8


< 0.1 0.4


g/cm³ 1.01 g/cm³ 0.91 g/cm³ 0.92 W/mK 0.29 W/mK 0.27 W/mK 0.26 W/mK 0.26 W/mK 0.30


1.65 1.40 1.47 0.79 0.50 0.44 0.43 0.51


Figure 3: Fired bulk density of CA6 based vibration castables 0 - 1 mm Reactive Alumina CL 370


CA-14 M CA-270


Bentonite


Carboxymethyl- cellulose


% 90 % %


% 10 % 0.5


% 0.5 % 63


0.04 41


PATCH SLA 2


50 20 30


water demand is reduced from 60% for VIB 1.1 to 43% for VIB 1.3.


Figure 4: Cold modulus of rupture of CA6


based vibration castables


Figure 5: Cold crushing strength of CA6


based vibration castables


The strength properties are further improved by partial substitution of Bonite instead of SLA-92. The higher strength of the dense Bonite grains when compared to the porous SLA-92 grains provides a stronger framework which results in higher dried and fired strengths.


The different castable concepts cover the range of 1 – 18 MPa for cold modulus of rupture at 110°C/24h and 3 – 38 MPa at 1500°C/5h. The cold crushing strength at 110°C/24h can be adjusted between 5 and 112 MPa and between 5 and 200 MPa after firing at 1500°C/5h. The highest strength values are achieved by the pure Bonite based castable VIB 2.7.


VIB 2.7


91 8


< 0.1 0.7


PATCH SLA 1


89 10


< 0.1 0.4


PATCH SLA 2


87 13


< 0.1 < 0.1


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NOVEMBER 2014 ISSUE


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