Refractories - Self Flowing and Pumpable Castable Refractories

Background

Another development related to the low cement line of castables is that of self-flowing or pumpable castables, this affording a new dimension in installation. In the past most castables were installed by gunning or casting, the latter requiring internal or external vibration for the placement of low cement castables to fill in behind forms.

Advantages of Self Flowing Castables

The ability of the new self-flowing castables to move behind forms and around anchors in difficult to reach areas is a great advantage in installation. Typically, internal or external vibration was necessary for the placement of the low cement type castables to fill behind forms. Additionally, these self-flowing or pumpable castables may be transported to high elevations.

Characteristics and Properties of Self Flowing Castables

With such high self-flowing characteristics, it might be anticipated that these products would have higher shrinkage after curing, drying, and firing than the regular low cement castables. However, by maintaining a low water content with proper mix design that avoids segregation, this is not true. In fact, similar procedures may be used for curing, drying, and firing as for regular castables. Sections through properly prepared self flow LCC reveal the high density and uniform texture of the grain structure. These castables will self flow under their own weight and easily fill intricate shapes. While these self-leveling castables utilize sizing and cement content similar to low cement and ultra low cement castables, many separate features have been optimised to generate the self-flowing property. The physical properties of three types of self-flow castables are shown in Table 1.

Table 1. Typical physical properties of self flowing castables.

Physical Property

Clay Based LCC

Bauxite Based LCC

Tabular Based LCC

Regular

Self Flow

Regular

Self Flow

Regular

Self Flow

Casting Water (%)

5.0

5.0

4.5

4.25

5.5

5.5

Set Time (hrs)

1.0

4.0

Bulk Density (pcf)

Poured

119

148

Vibrated

149

153

174

174

After 2010°F

189

190

After 2550°F

167

171

After 2910°F

167

168

After 3000°F

188

192

Cold Crush (psi)

Poured after 200°F

1700

10100

11600

15700

Vibrated after 200°F

8449

11399

11600

15700

After 2010°F

15300

5430

After 2550°F

11600

11600

After 2910°F

11150

17300

After 3000°F

21800

25100

Perm. Lin. Ch (%)

After 2010°F

0.0

0.0

After 2550°F

+0.1

+0.4

After 2910°F

+1.1

+0.5

After 3000°F

-0.2

-0.5

Chem. Analysis (%)

SiO2

Tr

Tr

Al2O3

76.0

76.0

94.0

94.0

CaO

1.1

1.1

1.1

1.1

Cr2O3

5.0

5.0

Applications

This self-flowing property of a castable is indeed an installation advantage and many manufacturers are adopting their castable product line to be self-flowing. These self-flowing castables are now being used, often times replacing brick, plastics, and conventional castables, in installations in ladles, aluminum furnaces in the upper sidewalls and roofs, ceramic kiln car decks and in the steel industry in ladle covers, tundish covers, tundish safety linings, and precast shapes. They are also used in rotary kilns as nose rings, lifters, firing hoods, coolers, preheater maintenance, and in incinerators in charging zones and burners. Other special mixes are used in the aluminum industry at or near metal contact in the lower sidewalls, hearths, ramps, and door skills/jambs.

Note – A complete list of references can be obtained by referring to the original text.

Primary author: Edwin Ruh

Source: Abstracted from International Ceramic Monographs, Vol. 1, no. 2, pp. 772-93, 1994.

For more information on this source please visit The Australasian Ceramic Society.

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