Insulating Firebrick Selection Guide: FJM, GMK23 & EcoFoam Compared

In the design, construction, and maintenance of high-temperature industrial furnaces, the selection of insulating firebrick (IFB) directly affects furnace-wall heat loss, structural steel loads, refractory lining life, and overall operating costs. Selecting the wrong brick—whether because of an insufficient temperature rating, excessive thermal conductivity, or unsuitable mechanical strength—can lead to overheating of the furnace shell, increased energy consumption, or even premature lining failure.

Firebird offers three major insulating firebrick product lines covering classification temperatures from 1260°C to 1760°C. These products support applications ranging from laboratory electric kilns to large industrial furnaces. This guide explains how to select among the three series by comparing their technical properties, forming processes, application areas, and cost-performance characteristics.

1. Understanding Insulating Firebrick Classification Standards

1.1 ASTM C155: A Globally Recognized Classification System

ASTM C155 is one of the most widely used international classification standards for insulating firebrick. It classifies IFBs according to the test temperature at which the permanent linear change after reheating does not exceed 2%.

The grade number indicates the approximate temperature in degrees Fahrenheit. For example, Grade 23 corresponds to 2300°F, or approximately 1260°C, while Grade 26 corresponds to 2600°F, or approximately 1430°C.

This classification system is widely recognized and provides a useful basis for international procurement and product comparison.

1.2 ISO 2245 and Chinese GB Standards

In addition to ASTM standards, ISO 2245:2006 and the Chinese standard GB/T 35845-2018 for mullite insulating firebrick are also widely used.

ISO 2245 uses a “temperature-density” designation. For example, ISO 2245-140-0.8 indicates a classification temperature of 1400°C and a bulk density of 0.8 g/cm³.

Chinese GB designations combine material initials, temperature grade, and density. For example, MG-26 corresponds approximately to ASTM Grade 26.

Although relationships exist among ASTM, ISO, and Chinese GB classifications, their test methods and individual property requirements are not identical. For international procurement, ASTM classifications are commonly used as the primary reference for comparison.

1.3 Classification Temperature Is Not the Same as Continuous Use Temperature

This is one of the most commonly misunderstood points in IFB selection.

Classification temperature is the test temperature at which the brick’s permanent linear change after reheating does not exceed 2%. It is not the temperature at which the brick can necessarily operate continuously over the long term.

Practical selection recommendations:

• Hot-face applications: Select a grade with a classification temperature approximately 200–300°C above the design temperature.
• Backup applications: Calculate the interface temperature based on the lining’s temperature gradient, then select a brick with a classification temperature approximately 100°C above the calculated interface temperature.

For example, if the furnace design temperature is 1200°C and the IFB is used directly on the hot face, ASTM Grade 26, with a classification temperature of 1430°C, should be considered instead of ASTM Grade 23, with a classification temperature of 1260°C. This provides a greater margin for long-term dimensional stability.

2. Overview of Firebird’s Three Insulating Firebrick Series

Firebird’s three IFB product lines use different forming processes and focus on different performance priorities. Together, they provide a broad density and temperature coverage matrix.

The following sections explain the technical characteristics and selection logic of each series.

3. FJM Mullite Insulating Firebrick Series

The FJM Series is Firebird’s main general-purpose IFB product line. It is manufactured from pure refractory clay, selected alumina, and graded organic fillers.

The bricks are formed through extrusion or casting, fired at high temperature in a natural-gas tunnel kiln, and precision-ground to achieve accurate dimensions. The series covers the full range from ASTM Grade 23 to Grade 32, making it suitable for a broad range of industrial furnace applications.

3.1 Key Features

• Full temperature coverage: Classification temperatures from 1260°C to 1760°C meet the requirements of most industrial furnaces.
• Good dimensional stability: High-purity raw materials and extended high-temperature firing help control permanent linear change.
• High mechanical strength: Extrusion gives the bricks relatively high compressive and flexural strength, making them suitable for load-bearing and self-supporting structures.
• Flexible dimensions: Standard straight bricks, arch bricks, wedge bricks, and special shapes can be manufactured.
• Low iron and low impurity content: Fe₂O₃ content ranges from approximately 0.4% to 1.0%, supporting stable performance under specified furnace atmospheres.

3.2 Main Grades and Typical Properties

The following values are typical properties of standard FJM grades. Thermal conductivity is tested using the ASTM C182 water-flow plate method.

Selection Highlight: FJM26LS

FJM26LS is a lightweight Grade 26 product with a bulk density of only 0.6 g/cm³, approximately 25% lower than standard FJM26. Its thermal conductivity remains 0.21 W/m·K at 400°C, the same listed value as standard FJM26.

This means FJM26LS can reduce furnace-wall weight and structural steel loads without sacrificing the listed insulation performance. Its Al₂O₃ content is 59%, compared with 55% for standard FJM26, providing additional chemical and high-temperature stability.

FJM26LS is suitable for furnaces where lining weight or heat-storage reduction is an important consideration.

3.3 FJM Series Selection Recommendations

• General-purpose selection: FJM26, with a bulk density of 0.8 g/cm³ and a classification temperature of 1430°C, offers competitive pricing and is one of the most widely produced mullite insulating firebricks.
• Lightweight lining: FJM26LS, with a bulk density of 0.6 g/cm³, reduces lining weight by approximately 25% while maintaining the listed thermal conductivity.
• High-strength or load-bearing positions: FJM26H, with a bulk density of 0.9 g/cm³, is suitable for areas such as ceramic-kiln roofs where higher mechanical strength is required.
• High-temperature applications: FJM28, FJM30, and FJM32 provide progressively higher temperature capabilities. FJM32 may be considered as an alternative to alumina bubble brick in selected applications above 1650°C.
• Hot-blast stove applications: FJM30S has a listed PLC of only -0.2% at 1600°C and is designed for iron and steel hot-blast stoves.

4. GMK23 Anorthite Insulating Firebrick

The GMK23 Series uses an innovative foamed-slurry casting process. Its principal raw materials include clay, calcium carbonate, and an organic foaming agent.

After high-temperature firing, the brick develops a composite structure containing anorthite (CaO·Al₂O₃·2SiO₂) and mullite (3Al₂O₃·2SiO₂). The organic foaming agent produces a fine, uniform pore structure, giving the brick very low thermal conductivity and good thermal-shock resistance.

4.1 Key Features

• Very low thermal conductivity: GMK23 has a listed thermal conductivity of only 0.12 W/m·K at a 400°C mean temperature, compared with 0.19 W/m·K for a conventional ASTM Grade 23 brick.
• Environmentally cleaner production: The organic foaming agent replaces traditional burnout materials such as sawdust and expanded polystyrene beads, resulting in no SO₂ emissions from these burnout materials. One cubic metre of organic foaming agent can replace up to 400 m³ of conventional burnout materials.
• Fine and uniform pores: Foam casting produces smaller and more uniform pores than conventional extrusion, helping reduce solid conduction, gas convection, and radiant heat transfer.
• Good thermal-shock resistance: The anorthite-mullite composite structure and microporous characteristics contribute to resistance against repeated heating and cooling.
• Resistance to alkali attack: The anorthite-containing composition provides relatively good resistance in environments containing alkali vapours.

4.2 Grades and Typical Properties

Note: Thermal conductivity is measured using the ASTM C182 water-flow plate method. “Traditional 23” represents typical values for a conventional extruded or cast ASTM Grade 23 brick and is included for comparison.

4.3 Comparison: GMK23 vs. Conventional ASTM Grade 23 IFB

GMK23 is positioned for comparison with JM23-, K23-, and BNZ23-type products from international brands.

Within the same ASTM Grade 23 classification, GMK23 has a listed thermal conductivity approximately 37% lower than the conventional brick shown in the table: 0.12 versus 0.19 W/m·K at 400°C. This difference primarily results from the finer and more uniform microporous structure created by the foamed-slurry casting process.

GMK23 also has a lower bulk density—0.5 g/cm³ compared with 0.6 g/cm³ for the conventional brick—helping reduce furnace-wall weight.

GMK23C is an upgraded version of GMK23. Its Al₂O₃ content increases from 37% to 48.5%, while its classification temperature increases from 1260°C to 1320°C, corresponding to ASTM Grade 24. It is intended for applications requiring a greater temperature margin, including higher-duty electric kilns and laboratory furnace linings.

Selection note: GMK23 has chemical, thermal, and physical properties comparable to JM23- and BNZ23-type products and may be considered as a replacement candidate under suitable operating conditions.

Final material selection depends on the operating temperature, lining position, furnace atmosphere, mechanical load, and heating cycle. Sample testing or a trial installation is recommended before making a final replacement decision.

4.4 Recommended Applications for GMK23

• Electric kilns and laboratory furnaces: Very low thermal conductivity and low heat storage support rapid heating and lower energy use in small furnaces.
• Semiconductor and electronic-material degassing furnaces: Cleaner production without SO₂ emissions from conventional burnout materials can support high-cleanliness requirements.
• Heat-treatment furnaces: Good thermal-shock resistance supports cyclic heating and cooling.
• Ceramic-kiln backup insulation: Suitable as backup insulation in roller kilns, tunnel kilns, and shuttle kilns.
• Alkali-vapour environments: The anorthite phase provides relatively good resistance to alkali attack.

5. EcoFoam RTGC Low-Thermal-Conductivity Insulating Firebrick

The EcoFoam RTGC Series uses a foam-cast microporous manufacturing process. Selected alumina, refractory clay, and organic foaming agents produce a fine and uniform microporous structure.

The series covers ASTM Grades 23 to 30, with classification temperatures from 1260°C to 1650°C. At relatively low density, it balances insulation performance, mechanical strength, and high-temperature dimensional stability.

EcoFoam RTGC is positioned as an IFB solution for energy-efficiency upgrades and performance improvements.

5.1 Key Features

• Microporous structure: Foam casting creates smaller and more uniform pores than conventional extruded IFB, helping reduce heat transfer.
• Low density combined with practical strength: The products reduce density while maintaining useful compressive and flexural strength, helping limit handling and installation damage.
• Controlled PLC: Good permanent linear change control helps reduce lining shrinkage, joint opening, and thermal-bridge risks during high-temperature operation.
• Relatively high refractoriness under load: RUL provides an additional operating margin for high-temperature linings subject to light mechanical loads.
• Environmentally cleaner production: Organic foaming agents replace conventional burnout materials, avoiding SO₂ emissions from those materials.

5.2 Grades and Typical Properties

5.3 Energy-Saving Potential

According to thermal simulation calculations, replacing conventional extruded insulating firebrick with EcoFoam low-thermal-conductivity IFB may save approximately 51 m³ of natural gas per square metre of furnace wall per year under the simulated conditions.

This corresponds to approximately RMB 2.9 per standard brick per year. Even if the initial brick cost is 50% higher, long-term fuel savings may still provide an attractive return on investment.

Actual energy savings depend on the furnace type, operating temperature, annual operating time, and complete furnace-wall construction.

5.4 Recommended Applications for EcoFoam RTGC

• Energy-efficiency upgrade projects: Lower thermal conductivity can reduce heat loss without increasing furnace-wall thickness.
• Heat-treatment furnaces: Suitable for annealing furnaces, carburizing furnaces, bogie-hearth furnaces, and pit furnaces where thermal-shock resistance and low heat storage are important.
• Iron and steel industry: Insulating linings for hot-blast stoves, reheating furnaces, and annealing furnaces.
• Ceramic kilns: Roller kilns, tunnel kilns, shuttle kilns, and kiln cars.
• Lithium-battery material kilns: Selected areas of cathode- and anode-material kilns after evaluating furnace atmosphere and contamination requirements.
• Aluminium industry: Anode-baking furnaces and selected backup insulation areas.

6. Key IFB Selection Parameters

Regardless of the product series, the following six parameters are central to IFB selection. Understanding their engineering significance helps avoid the common mistake of selecting a brick based only on temperature.

6.1 Classification Temperature and Operating Temperature

As explained above, classification temperature is the laboratory test temperature at which permanent linear change after reheating does not exceed 2%. It is not the same as a recommended continuous operating temperature.

The selection process should account for the brick’s position in the lining—hot face or backup—and include an appropriate margin above the calculated design or interface temperature.

This is the first selection step: determine the required temperature grade before comparing other properties.

6.2 Thermal Conductivity

Thermal conductivity directly influences heat loss through the furnace wall and is one of the most important energy-efficiency parameters for insulating firebrick.

Important considerations include:

• Mean temperature: Thermal conductivity normally increases as temperature rises. Every quoted value should identify the corresponding mean temperature.
• Test method: The water-flow plate methods used in ASTM C182 and YB/T 4130 may produce results different from the parallel hot-wire method in ISO 8894. The hot-wire method commonly gives higher values. Only values measured using comparable methods should be compared.
• Relationship with density: Within the same temperature grade, a lower-density brick generally has lower thermal conductivity, but it may also have lower mechanical strength.

6.3 Bulk Density

Bulk density affects three key areas:

• Thermal conductivity, where lower density is generally beneficial
• Mechanical strength, where higher density is generally beneficial
• Structural load, where a lighter lining is generally beneficial

Selection therefore requires a balance among insulation performance, mechanical strength, and lining weight.

• Conventional extrusion processes have difficulty achieving a density below 0.6 g/cm³. For lower-density products, foam-cast GMK23 or EcoFoam products should be considered.
• The normal density tolerance is approximately ±0.05 g/cm³, and quotations are generally calculated using the theoretical density.
• For the same Grade 26 classification, a brick with a density of 0.9 g/cm³ is approximately 10% more expensive than a brick with a density of 0.8 g/cm³.

6.4 Compressive and Flexural Strength

Cold crushing strength affects transportation, installation, and lining durability. Hot strength influences the range of suitable operating conditions.

The selection principle is to choose sufficient strength for the application rather than automatically pursuing the highest possible strength. Excessive strength often comes with greater density and higher thermal conductivity.

Key considerations include:

• Roof and load-bearing positions: Higher strength is required. One example is FJM26H, with a bulk density of 0.9 g/cm³ and a listed cold crushing strength of 2.8 MPa.
• Backup insulation: Strength requirements are lower, so low-density products such as GMK23, with a bulk density of 0.5 g/cm³ and a listed CCS of 1.0 MPa, may be suitable.
• Bricks pressed directly to final dimensions may have higher strength than bricks that are cut and ground. Some overseas products use direct forming.

6.5 Permanent Linear Change

Permanent linear change reflects the dimensional stability of a brick during extended high-temperature exposure. It directly affects lining joints and sealing performance.

Important considerations include:

• PLC is normally negative, indicating shrinkage. Greater negative values indicate a higher shrinkage risk.
• Mullite IFB generally requires PLC to remain within 1%. Some grades can be controlled within 0.5%.
• Tighter guaranteed values normally increase cost, so dimensional accuracy and price should be balanced according to project requirements.
• Some products may exhibit positive PLC, indicating expansion. This can be associated with mechanisms such as secondary mullitization and should be evaluated together with XRD analysis.

6.6 Chemical Composition and Furnace-Atmosphere Compatibility

Chemical composition provides a foundation for material performance, but it should not be used as the only criterion for determining whether one brick is better than another.

Key considerations include:

• Al₂O₃: Higher alumina content generally supports improved high-temperature performance. Alumina powder is normally added to grades above ASTM Grade 26.
• Fe₂O₃: Lower iron content generally indicates higher raw-material purity. However, higher iron content may also increase brick strength through the formation of lower-melting phases.
• Atmosphere compatibility: Reducing atmospheres containing H₂ or CO require low iron and low impurity levels. Oxidizing atmospheres are generally less restrictive.
• CO resistance: Blast-furnace gas contains CO, so IFBs used in hot-blast stoves should be evaluated for their CO-resistance classification.
• Alkali-vapour environments: Ceramic and glass furnaces may contain alkali vapours. The alkali resistance of anorthite-containing products such as GMK23 should therefore be considered.

7. Comparison and Selection of the Three IFB Series

7.1 Thermal-Conductivity Comparison at Equivalent Grades

The following table compares the three product series at ASTM Grades 23 and 26, two of the most commonly used classifications.

All listed values are based on the ASTM C182 water-flow plate method to support a more consistent comparison.

Comparison conclusions:

• Grade 23: GMK23 has the lowest listed thermal conductivity at 400°C—0.12 W/m·K—which is approximately 37% lower than FJM23.
• Grade 26: RTGC26-06 achieves lower listed thermal conductivity at a lower density: 0.17 versus 0.21 W/m·K at 400°C, with densities of 0.60 versus 0.80 g/cm³. Its listed compressive strength is 2.5 versus 2.5 MPa.
• Strength: The FJM Series generally provides higher strength within equivalent grades and is suitable for load-bearing positions.
• Maximum classification temperature: The FJM Series covers grades up to 1760°C, GMK23 up to 1320°C, and EcoFoam RTGC up to 1650°C.

7.2 IFB Selection Process

The following selection process is recommended for practical furnace projects:

1. Determine the required temperature grade.
   Identify the maximum furnace design temperature and the brick’s position as either hot-face or backup insulation. Use an appropriate temperature margin, typically 200–300°C for hot-face applications.
2. Determine the lining position.
   Hot-face bricks must be evaluated for mechanical strength, furnace atmosphere, and thermal shock. Backup bricks place greater emphasis on thermal conductivity and cost.
3. Evaluate density and structural limitations.
   Determine whether the furnace steel structure has a load limitation and whether minimum heat loss is a primary objective.
4. Match the requirements with the appropriate product series.
   • High strength, full temperature coverage, and standard dimensions → FJM Series
   • Very low thermal conductivity, environmentally cleaner production, and low weight within the 1260–1320°C range → GMK23 Series
   • Low density combined with practical strength, quantifiable energy-saving potential, and ASTM Grades 23–30 → EcoFoam RTGC Series
5. Verify and confirm.
   Request the TDS, confirm the applicable test methods, and arrange sample testing where necessary.

8. IFB Selection Recommendations by Industry

8.1 Ceramic Kilns

Ceramic kilns—including roller kilns, tunnel kilns, and shuttle kilns—are among the largest application areas for insulating firebrick.

Roller and tunnel kilns commonly operate between 1200°C and 1450°C and require good dimensional accuracy and high-temperature volume stability.

• Kiln roof: FJM26H, with a density of 0.9 g/cm³ and higher strength, or FJM26, with a density of 0.8 g/cm³
• Sidewall hot face: FJM26 or EcoFoam RTGC26 as an energy-efficiency upgrade
• Backup insulation: GMK23 for very low thermal conductivity or EcoFoam RTGC23
• Kiln cars: EcoFoam RTGC26-06 for low density and low heat storage, helping reduce heat absorbed by the kiln car

8.2 Glass Furnaces

Glass furnaces operate at high temperatures, commonly between 1500°C and 1600°C. Some areas may also be exposed to alkali vapour attack.

Insulating firebrick is mainly used in applications such as tin-bath roof insulation, crown backup insulation, and bottom insulation layers.

• Tin-bath roof insulation: FJM23/26 with a density of approximately 0.6 g/cm³ or low-thermal-conductivity EcoFoam RTGC23
• Crown backup insulation: FJM26/FJM28
• Bottom insulation layer: FJM26 or FJM26LS

8.3 Iron and Steel Industry

In the iron and steel industry, IFBs are commonly used in hot-blast stove domes, walls and hot-air pipes, as well as in reheating furnaces.

PLC requirements are particularly important in hot-blast stoves.

• Hot-blast stove dome and walls: FJM30S, with a listed PLC of only -0.2% at 1600°C and a design focused on hot-blast stove applications
• Reheating-furnace backup insulation: FJM26 or EcoFoam RTGC26
• Annealing furnaces: EcoFoam RTGC26/28 for thermal-shock resistance and low heat storage

8.4 Aluminium Melting and Holding Furnaces

Aluminium holding furnaces commonly operate between 800°C and 1100°C.

The main considerations are controlling furnace-wall heat loss and ensuring that the insulating firebrick is isolated from direct contact with molten aluminium.

• Furnace-wall hot face outside molten-aluminium contact areas: FJM23 or GMK23
• Backup insulation: GMK23 for very low thermal conductivity or EcoFoam RTGC23

8.5 Electric Kilns and Laboratory Furnaces

Electric kilns and laboratory furnaces are normally compact, heat rapidly, and operate in cycles. Low heat storage and low heat loss are therefore particularly important.

• Preferred option: GMK23. Its listed thermal conductivity of 0.12 W/m·K at 400°C, density of 0.5 g/cm³, and low heat storage support rapid heating and lower energy consumption.
• For higher operating temperatures: GMK23C, with a classification temperature of 1320°C, or EcoFoam RTGC26-06
• For a greater temperature margin: EcoFoam RTGC28, with a classification temperature of 1540°C

8.6 Petrochemical Furnaces

Petrochemical process heaters, cracking furnaces, and reformers cover a wide operating-temperature range. Some applications involve reducing atmospheres containing H₂ or CO.

• Process-heater walls: FJM26/FJM28 as standard options
• Reducing atmospheres: FJM28/30, with higher Al₂O₃ and lower Fe₂O₃
• Energy-efficiency upgrades: EcoFoam RTGC26/28 to replace conventional extruded IFB and reduce heat loss

8.7 Lithium-Battery Material Kilns

Kilns used to calcine lithium-battery cathode and anode materials require controlled atmospheres, good temperature uniformity, and careful contamination management.

• Secondary-sintering kilns: FJM28L, a low-density ASTM Grade 28 brick with a density of 0.8 g/cm³
• Backup insulation: EcoFoam RTGC26-06 or GMK23

9. Frequently Asked Questions

Q1: What is the classification temperature of an insulating firebrick, and how is it different from the operating temperature?

Classification temperature is the test temperature at which the permanent linear change of the insulating firebrick after reheating does not exceed 2%.

For example, ASTM Grade 23 corresponds to a test temperature of 1230°C and a classification temperature of 1260°C. This does not mean the brick can necessarily be used continuously at 1260°C.

For hot-face applications, select a grade with a classification temperature approximately 200–300°C above the furnace design temperature. For backup applications, select a grade with a classification temperature approximately 100°C above the calculated interface temperature.

Q2: What are the main differences among FJM, GMK23, and EcoFoam insulating firebricks?

The main differences are their forming processes and performance priorities.

The FJM Series uses extrusion or cast forming and covers the full ASTM Grade 23–32 range, corresponding to classification temperatures from 1260°C to 1760°C. It is a general-purpose product line offering relatively high strength and a complete grade range.

GMK23 uses foamed-slurry casting and has a very low listed thermal conductivity of 0.12 W/m·K at 400°C. It is suitable for energy-sensitive low- and medium-temperature applications between approximately 1260°C and 1320°C.

EcoFoam RTGC uses a foam-cast microporous structure and balances low density, strength, and insulation performance. It covers ASTM Grades 23–30, corresponding to classification temperatures from 1260°C to 1650°C, and is suited to energy-efficiency upgrades requiring balanced performance.

Q3: Can thermal-conductivity values measured using different test methods be compared directly?

No.

The water-flow plate methods used in ASTM C182 and YB/T 4130 and the parallel hot-wire method used in ISO 8894 normally produce different results. The hot-wire method generally gives higher values.

When comparing thermal conductivity among different suppliers, confirm that the test standards, methods, sample conditions, and mean test temperatures are consistent.

The EcoFoam Series provides both YB/T 4130 data and ASTM C182 data tested by ICAR in France. Use the data set required by your procurement specification.

Q4: Can GMK23 anorthite insulating firebrick replace Morgan JM23?

GMK23 has chemical, thermal, and physical properties comparable to JM23- and BNZ23-type products and may be considered as a replacement candidate under suitable operating conditions.

Its listed thermal conductivity of 0.12 W/m·K at 400°C is lower than the value shown for a conventional JM23-type product.

However, final material selection depends on the operating temperature, lining position, atmosphere, mechanical load, and heating cycle. Sample testing or a trial installation is recommended before making a final replacement decision.

Q5: Is a lower bulk density always better for insulating firebrick?

Not necessarily.

Lower density generally means lower thermal conductivity and lower heat storage, which can improve energy efficiency. However, it may also reduce compressive strength and increase permanent linear change.

Selection should consider the lining position, whether the brick is used on the hot face or as backup insulation, the mechanical-load requirements, and the required temperature grade.

Conventional extrusion has difficulty producing bricks with a density below 0.6 g/cm³. For lower-density products, foam-cast GMK23 or EcoFoam grades should be considered.

The correct approach is to balance insulation performance with mechanical strength.

Q6: How should the correct ASTM IFB grade be selected?

Use the following process:

1. Determine the maximum furnace design temperature.
2. Determine whether the brick will be used on the direct hot face or as backup insulation.
3. For hot-face applications, select a classification temperature at least 200–300°C above the design temperature.
4. For backup applications, calculate the interface temperature and select a classification temperature approximately 100°C above it.

For example, if the furnace design temperature is 1200°C, ASTM Grade 26, with a classification temperature of 1430°C, should be considered for the hot face instead of ASTM Grade 23, with a classification temperature of 1260°C.

10. Conclusion

Insulating firebrick selection is not simply a matter of matching one temperature with another. It is a systematic engineering decision that must consider temperature classification, thermal conductivity, bulk density, mechanical strength, permanent linear change, furnace-atmosphere compatibility, and cost-effectiveness.

Firebird’s three product lines can be summarized as follows:

• FJM Series: Full temperature coverage, strength-oriented design, and flexible dimensions for standard applications across a wide range of industrial furnaces
• GMK23 Series: Very low thermal conductivity and environmentally cleaner production for electric kilns, laboratory furnaces, and low- to medium-temperature energy-saving applications
• EcoFoam RTGC Series: A microporous structure and balanced performance for energy-efficiency upgrades requiring both mechanical strength and thermal insulation

The three series are not competing alternatives. They form a complementary product matrix.

Different products can be used in different parts of the same furnace to create a more effective lining system. For example, FJM26H may be used on the hot face where strength is required, GMK23 may be used as backup insulation to reduce heat transfer, and EcoFoam RTGC26-06 may be used in the kiln car to reduce heat storage.

Need Professional IFB Selection Support?

The Firebird technical team can recommend suitable products based on your furnace type, operating temperature, atmosphere, lining position, and energy-efficiency objectives. Sample testing support is also available.

Contact us for an IFB selection recommendation:

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