Refractories - Low Cement, Ultra Low Cement and No Cement Castable Refractories

Background

When it was discovered that the addition of highly reactive volatilised or fume silica to a castable would dramatically change the physical properties, a new family of castables resulted. These dense strong refractory castables, based on the use of low calcium aluminate cement content, have replaced many conventional castables, plastics, ramming and gunning mixes and are used in many applications that require high refractoriness, corrosion resistance and abrasion resistance. These castables possess a uniform structure with low porosity; have high temperature strength throughout the low and intermediate temperature range. Today virtually every refractory castable manufacturer has a complete line of these low cement castables, ultra-low cement and no cement castables.

Classifications

These three types of castables have been classified by ASTM as:

        Low Cement containing 1.0% to 2.5% CaO

        Ultra-Low Cement 0.2% to 1.0% CaO

        No Cement Castables with up to 0.2% CaO.

Physical Properties

Typical properties for these three types are shown in Table 1, Table 2 and Table 3.

Table 1. Typical physical properties of low cement castables (LCC).

Physical Property

Vitreous Silica LCC

45% Al2O3 LCC

60% Al2O3 LCC

70% Al2O3 LCC

80% Al2O3 LCC

Bulk Density (pcf)

129

143

153

158

173

Modulus of Rupture (psi)

After 230°F

1450

1530

1760

1990

1850

After 1500°F

1000

1700

2550

3300

2300

At 2500°F

2230

640

750

250

Cold Crush (psi)

After 230°F

12600

17070

18800

21700

20800

After 1500°F

11800

13230

13670

15000

14500

Perm. Lin. Ch (%)

After 230°F

Neg.

Neg.

Neg.

Neg.

Neg.

After 1500°F

-0.1

-0.3

-0.2

-0.2

-0.2

After 2300°F

-0.2

After 2700°F

+2.0

After 3000°F

-0.7

+1.6

+2.5

Chem. Analysis (%)

SiO2

75.0

48.4

35.0

27.0

11.4

Al2O3

21.6

45.6

59.5

67.3

82.0

TiO2

0.5

2.2

2.0

2.4

2.8

Fe2O3

0.3

0.7

1.0

0.9

1.3

CaO

2.1

2.4

2.2

2.1

2.2

MgO

0.1

0.2

0.1

0.1

0.1

Alk. (Na2O+K2O)

0.3

0.5

0.2

0.2

0.2

Max. Serv. Temp (°F)

2000

2700

3100

3100

2900

Table 2. Typical physical properties of ultra low cement castables (ULCC).

Physical Property

45% Al2O3 ULCC

60% Al2O3 ULCC

70% Al2O3 ULCC

80% Al2O3 ULCC

95% Al2O3 ULCC

Bulk Density (pcf)

146

156

156

171

183

Modulus of Rupture (psi)

After 230°F

850

1320

1080

1150

880

After 1500°F

1450

2770

2770

1500

1590

Cold Crush (psi)

After 230°F

4800

7950

6250

5600

4100

After 1500°F

11510

14200

11470

7000

8960

Hot MOR (psi)

At 2700°F

340

700

540

430

720

Perm. Lin. Ch (%)

After 1500°F

-0.1

-0.2

-0.2

-0.1

0.0

After 2700°F

+0.2

After 3000°F

-0.6

-0.3

+1.2

After 3140°F

-0.7

Chem. Analysis (%)

SiO2

49.5

31.6

27.5

16.4

6.8

Al2O3

46.0

64.0

67.9

78.9

92.5

CaO

1.0

0.9

0.9

0.9

0.5

Table 3. Typical physical properties of no low cement castables (NCC).

Physical Property

65% Al2O3 NCC

85% Al2O3 NCC

95% Al2O3 NCC

Bulk Density (pcf)

156

174

188

Modulus of Rupture (psi)

After 230°F

1560

1820

1380

After 1500°F

1950

1760

2870

At 2700°F

550

820

1570

Cold Crush (psi)

After 230°F

6300

8550

5340

After 1500°F

8990

9500

12850

Perm. Lin. Ch (%)

After 1500°F

0.0

0.0

0.0

After 3000°F

-0.6

+1.1 (3140)

+0.2 (3300)

Chem. Analysis (%)

SiO2

31.5

9.6

5.1

Al2O3

64.2

85.5

94.2

CaO

0.1

0.2

0.1

Max. Serv. Temp (°F)

3100

3200

3300

Applications

These low cement-type castables find many applications through industry including the steel, iron and steel foundries, aluminum furnaces and other non-ferrous metals, rotary kilns, incinerators and also for making precast shapes. The strength which are developed in these castables are often equal to or greater than fired products.

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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