Raw materials based on Al2O3, SiO2 and CaO. CaO is typically used for anorthite refractory bricks. Raw materials are clay, kaolin, kyanite, mullite, (light) chamotte, sillimanite or andalusite. Alumina, alumina hydrate and corundum in the form of hollow sphere corundum are also used for refractory bricks with high classification temperature. The thermal conductivity is defined by the total porosity as well as pore shape and pore size distribution. The porosity is produced by burnout materials and water. Burnout materials are e.g. Sawdust, styrene bubbles, coke or cellulose.

Shaping and firing of insulating fire bricks

Raw materials and burnout materials are optionally mixed dry and/or mixed with water. The amount of water depends on the shaping process. The bricks are formed by casting, slingering, extrusion or dry pressing. For the casting process large molds are used and blocks/hoppers are casted. The casting compounds are processed directly after mixing. Water-binding raw materials extract water from the slurry and support the setting of the green body. The process can be accelerated by adding gypsum or cement. Due to the high water content, the drying of the green compacts takes a correspondingly long time. Light weight bricks with high porosity can be produced this way. In addition, foam or foaming agent can be added to increase the amount of pores. Soap or saponins are used as foams, while metal or carbide powders are used as foaming agents in the processes.

The slingering process is a continuous process in which the masses are slingered in large molds or on a conveyor belt.  Insulating fire bricks of medium density can be produced this way.

Masses which are used for the extrusion process, undergo mulling after mixing. Water-apsorbing raw materials can saturate with water till an uniform moisture is reached in the mixture. The masses are then extruded through a mouthpiece, cut to size and dried.

Dry pressing is usually done uniaxial. The pressing method is suitable for the production of bricks with a high density.

The shaping process and the porosity agents cause typical structures of the insulating fire bricks. 

Firing of the refractory bricks is done in shuttle or tunnel kilns. The firing temperature is equal to the specified classification temperature. The refractory bricks shrink during drying as well as during firing.  They have to be cut and grinded to final size after firing.

Properties

The properties of the aluminumsilicate refractory bricks result from the chemical composition, the pore formers/density and the firing temperature. Higher Al₂O₃ content and higher firing temperature of the firebricks result in higher the classification temperature. Classification temperature is the temperature at which a shaped refractory material is allowed to shrink by a maximum of 2% after 24 hours of firing. The upper application temperature of the materials is usually about 100K below the classification temperature.

The thermal conductivity of the final product depends on the chemical composition, density and pore structure. Insulating firebricks with low density and fine pore structure have a low thermal conductivity. The pore structure and density are largely determined by the manufacturing process. Fine burnout materials and a high water content in the process lead to a finer structure of the firebrick. This can be supported by using a foam/foaming agent. However, the density cannot be reduced endless. There must be sufficient structure in the green body to dry and burn it crack-free.The diagramm shows typical thermal conductivities of different IFB groups.

However, a low density goes ahead with a low strength of the insulating fire brick. The cold compressive strength is specified as a characteristic value. The “hot” properties of the material must be good enough to support walls and arches at the desired application temperature. Hot bending strength or creep under load are characteristic values for the use at high temperatures.

Thermal shock resistance limits the heating and cooling rates. This is especially important for periodically operated furnaces as well as operating furnace doors.

The measurement of these properties is standardized by the series of standards DIN EN 993 1-18, which are closely based on the corresponding ISO standards.

Classification of insulating fire bricks

ASTM C155

Refractory bricks are classified into different groups according to ASTM C155. The grouping results from the classification temperature and the density of the insulating fire bricks. Refractory bricks of a certain class may not exceed a defined density and may not exceed a shrinkage of 2% after firing for 24 hours. The test temperature is 30 K below this classification temperature.

Group	Shrinkage <2% after 24h at		Maximum density
	°F	°C	lb/ft²	kg/m³
Group 16	1550	845	34	545
Group 20	1950	1065	40	641
Group 23	2250	1230	48	769
Group 26	2550	1400	54	865
Group 28	2750	1510	60	961
Group 30	2950	1620	68	1089
Group 32	3150	1730	95	1522
Group 33	3250	1790	95	1522

ISO 2245 und EN 1094-2

The classification according to ISO 2245 and EN 1094-2 is also based on classification temperature (CT) and density. Shrinkage may not exceed 2% after 24h of firing at classification temperature.

Group	Shrinkage <2% after 24h at	Maximum density
	°C	kg/m³
Group 75	750	0,4
Group 80	800	0,5
Group 85	850	0,55
Group 90	900	0,6
Group 95	950	0,65
Group 100	1000	0,65
Group 105	1050	0,65
Group 110	1100	0,7
Group 115	1150	0,7
Group120	1200	0,7
Group 125	1250	0,75
Group130	1300	0,8
Group 135	1350	0,85
Group 140	1400	0,9
Group 150	1500	0,95
Group 160	1600	1,15
Group 170	1700	1,35
Group 180	1800	1,6

Shapes and Sizes

There are different standard shapes for insulating fire bricks depending on the application.

Square shapes

Rectangular formats (standard squares/straights) are called NF or N format and are used for straight walls. There are also bonders (B), double straights (D) and whelps/strechter (L) formats to lay a correct masonry bond:

Designation	Mark	dimensions in mm			Volume
		l	b	h	dm³
Standard squares	1	230	114	64	1,68
	2	250	124	64	1,98
	3	300	150	64	2,88
	1-76	230	114	76	1,99
	2-76	250	124	76	2,36
	3-76	300	150	76	3,42
Bonders	1 B	230	172	64	2,53
	2 B	250	187	64	2,99
	3 B	300	225	64	4,32
	1 B-76	230	172	76	3,01
	2 B-76	250	187	76	3,55
	3 B-76	300	225	76	5,13
Double straights	1 D	230	230	64	3,39
	2 D	250	250	64	4,00
	3 D	300	300	64	5,76
	1 D-76	230	230	76	4,02
	2 D-76	250	250	76	4,75
	3 D-76	300	300	76	6,84
Whelps	1 L	345	114	64	2,52
	2 L	375	124	64	2,98
	3 L	450	150	64	4,32
	1 L-76	345	114	76	2,99
	2 L-76	375	124	76	3,53
	3 L-76	450	150	76	5,13

Download straights as PDF

Arch bricks

Side arches (H), keys (Q), end arches (G), double end arches (GG) and end arch bonders (GB) are used for arches and round wall shapes. The radius in the table is calcualted for 2 mm joints.

Designation	Mark	Dimensions in mm					Volume
		a	b	h	l	r1)	dm³
Side arches	1 H   6	67	61	114	230	1197	1,68
	1 H 10	69	59	114	230	695	1,68
	1 H 16	72	56	114	230	413	1,68
	1 H 24	76	52	114	230	257	1,68
	1 H   6-76	79	73	114	230	1425	1,99
	1 H 10-76	81	71	114	230	832	1,99
	1 H 16-76	84	68	114	230	499	1,99
	1 H 24-76	88	64	114	230	314	1,99
	2 H   6	67	61	124	250	1302	1,98
	2 H 10	69	59	124	250	756	1,98
	2 H 16	72	56	124	250	450	1,98
	2 H 24	76	52	124	250	279	1,98
Keys	1 Q 10	119	109	230	64	2553	1,68
	1 Q 14	121	107	230	64	1791	1,68
	1 Q 28	128	100	230	64	838	1,68
	1 Q 50	139	89	230	64	419	1,68
	1 Q 10-76	119	109	230	76	2553	1,99
	1 Q 14-76	121	107	230	76	1791	1,99
	1 Q 28-76	128	100	230	76	838	1,99
	1 Q 50-76	139	89	230	76	419	1,99
	2 Q 10	129	119	250	64	3025	1,98
	2 Q 14	131	117	250	64	2125	1,98
	2 Q 28	138	110	250	64	1000	1,98
	2 Q 50	149	99	250	64	505	1,98
1) Radius with 2 mm joint

Download side arches and keys as PDF

Designation	Mark	Dimensions in mm					Volume
		a	b	h	l	r1)	dm³
End arches	1 G   4	66	62	230	114	3680	1,68
	1 G 10	69	59	230	114	1403	1,68
	1 G 16	72	56	230	114	834	1,68
	1 G 24	76	52	230	114	518	1,68
	1 G   4-76	78	74	230	114	4370	1,99
	1 G 10-76	81	71	230	114	1679	1,99
	1 G 16-76	84	68	230	114	1006	1,99
	1 G 24-76	88	64	230	114	633	1,99
	2 G   4	66	62	250	124	4000	1,98
	2 G 10	69	59	250	124	1525	1,98
	2 G 16	72	56	250	124	906	1,98
	2 G 24	76	52	250	124	563	1,98
Double arch bricks	1 GG   4	66	62	230	230	3680	3,39
	1 GG 10	69	59	230	230	1403	3,39
	1 GG 16	72	56	230	230	834	3,39
	1 GG 24	76	52	230	230	518	3,39
	1 GG   4-76	78	74	230	230	4370	4,02
	1 GG 10-76	81	71	230	230	1679	4,02
	1 GG 16-76	84	68	230	230	1006	4,02
	1 GG 24-76	88	64	230	230	633	4,02
	2 GG   4	66	62	250	250	4000	4,00
	2 GG 10	69	59	250	250	1525	4,00
	2 GG 16	72	56	250	250	906	4,00
	2 GG 24	76	52	250	250	563	4,00
End arch bonder	1 GB   4	66	62	230	172	3680	2,53
	1 GB 10	69	59	230	172	1403	2,53
	1 GB 16	72	56	230	172	834	2,53
	1 GB 24	76	52	230	172	518	2,53
	1 GB   4-76	78	74	230	172	4370	3,01
	1 GB 10-76	81	71	230	172	1679	3,01
	1 GB 16-76	84	68	230	172	1006	3,01
	1 GB 24-76	88	64	230	172	633	3,01
	2 GB   4	66	62	250	187	4000	2,99
	2 GB 10	69	59	250	187	1525	2,99
	2 GB 16	72	56	250	187	906	2,99
	2 GB 24	76	52	250	187	563	2,99
1) Radius with 2 mm joint

Download Arch bricks as PDF

Links and Literature

Books:

[amazon_link asins=’3802731638,3802731654,3802731689,3802731662,380273159X,3709186234,3662117428′ template=’ProductCarousel’ store=’insulatione02-21′ marketplace=’DE’ link_id=’83682644-2512-11e8-bbae-bb13e0718c37′]

Health and Safety:

TRGS 559 “Mineralischer Staub”: https://www.baua.de/DE/Angebote/Rechtstexte-und-Technische-Regeln/Regelwerk/TRGS/TRGS-559.html

Standards for refractory bricks:

ISO 2245: https://www.iso.org/standard/38367.html

ASTM C155: https://www.astm.org/Standards/C155.htm

EN 993-1: https://www.beuth.de/de/norm/din-en-993-1/2525981

EN 1094-2: https://www.beuth.de/de/norm/din-en-1094-2/8541498

JIS R2611: https://infostore.saiglobal.com/en-gb/Standards/JIS-R-2611-2001-799588/