Integrated furnace brick selection in 2026: Don’t just focus on the Al₂O₃ content

After working in the high-temperature kiln industry for more than ten years, I have observed one thing: when many purchasing and technical personnel select one-piece furnace bricks, the most common question they ask is - "What is the content of aluminum oxide (Al₂O₃)?"

68%, 75%, 80%...the higher the number, the more secure it seems.

But to be honest, choosing a brick based on its Al₂O₃ content is like buying a car based only on its engine displacement. Large displacement does not necessarily mean stable running, and high content does not necessarily mean durability. Today we will talk about, in addition to the composition report, when choosing integrated furnace bricks in 2026, you should also look at several more critical indicators.

1. Why is the "Al₂O₃ theory" unreliable?

Aluminum oxide (Al₂O₃) content does matter. It directly affects the load softening temperature and corrosion resistance of refractory materials. The higher the content, the better the high temperature resistance in theory.

But the problem is: most of the failures of hearth bricks are not "burned", but "peeled off" or "cracked by thermal shock".

For example, some high-alumina bricks have an Al₂O₃ content of more than 80%, but their thermal shock resistance is very poor. When the kiln is stopped and started, the temperature difference reaches hundreds of degrees Celsius. The internal stress of the bricks has no time to be released, and they directly crack. When a brick cracks, the surrounding bricks loosen and then begin to fall out piece by piece.

On the other hand, some bricks have an Al₂O₃ content of only about 65%, but because they added an appropriate amount of toughening phase and optimized the particle gradation, they have been running in kilns that frequently start and stop for more than two years without any problems.

Therefore, the Al₂O₃ content is a reference, but not necessarily a standard for material selection.

2. When choosing integrated furnace bricks, it is recommended to look at these five core indicators.

We compiled a set of selection comparison tables based on feedback from multiple on-site projects in 2025-2026. You can think of these five dimensions as a "score card" and check the samples or supplier reports you have one by one.

Indicator 1: Volume density (g/cm³)

Why watch this: Volume density reflects the density of the brick body. The higher the density, the lower the porosity, and the stronger the resistance to slag erosion and penetration.

How to judge: The volume density of integrated furnace bricks of the same brand differs by 0.1-0.2g/cm³, and the service life may differ by 30%. Require suppliers to provide actual measured values ​​rather than "typical values".

Reference range: 2.6-2.8 in ordinary areas, ≥2.9 is recommended in high temperature zones or areas with severe erosion.

Index 2: Apparent porosity (%)

Reference significance: The pores are channels for slag penetration. If the apparent porosity is too high, acid and alkali substances generated during the operation of the kiln will penetrate into the brick body through the pores, destroying the brick structure from the inside out.

Judgment method: The lower the apparent porosity value, the better. However, it should be noted that some manufacturers add excessive amounts of fine powder simply to reduce porosity, which will actually reduce the thermal shock resistance of the product. This indicator needs to be well balanced.

Reference range: One-piece bricks are generally controlled between 15% and 18%. Be cautious if it is less than 12%, as it may be too brittle.

Index 3: Normal temperature compressive strength (MPa)

Why watch this: This is one of the most important indicators in traditional selection. It reflects the brick"s ability to withstand static pressure loads.

How to judge: It’s good to have a high value, but you don’t have to pursue it blindly. Because in the actual furnace, the bricks mainly bear not "pressure", but "thermal stress" and "mechanical impact". As long as the compressive strength meets the standard, there is no need to spend 30% more of your budget to buy a value that is 50% higher.

Reference range: 40-60MPa is sufficient for ordinary kilns; ≥70MPa is recommended for large rotary kilns or heavy-load areas.

Index 4: Thermal shock stability (number of times)

Why watch this: This is one of the most overlooked, but actually most important, indicators for choosing integrated furnace bricks in 2026. It directly determines how long the bricks can last without cracking under the conditions of frequent starts and stops of the kiln and large temperature fluctuations.

Judgment method: Ask the supplier for 1100°C water-cooling and air-cooling cycle test data. The more tests, the better the performance. If the supplier says that it has not done this test, or that the indicator is irrelevant, you can directly choose another partner.

Reference range: Under normal working conditions, the number of 1100°C water cooling cycles needs to be no less than 15 times; for kilns that frequently start and stop, it is recommended that the number of cycles be no less than 25 times.

Indicator 5: Reheat line change rate (%)

Why watch this: This indicator tells you whether bricks will "shrink" or "expand" under high temperatures. If the expansion rate is not well controlled, the brick joints will be squeezed open; if the shrinkage rate is too large, gaps will appear between bricks, and the hot air flow will directly wash away the insulation layer behind.

How to judge: It is required to measure the linear change rate after burning at 1500℃×2h. The smaller the positive and negative values, the more stable it is.

Reference range: Within ±0.3% is considered good, within ±0.5% is acceptable, and exceeding ±0.8% is recommended to be cautious.

3. Different working conditions, different emphasis

There is no one type of brick that fits all kilns. I have listed three common working conditions and the corresponding selection focuses, so you can make the right choice.

Working condition type, typical furnace type, priority index, secondary index, index that can be appropriately relaxed

High temperature and strong erosion hazardous waste rotary kiln and non-ferrous smelting furnace apparent porosity (low) + Al₂O₃ content (high) volume density and normal temperature compressive strength

Frequent start and stop active lime kilns and intermittent kilns Thermal shock resistance Refire line change rate (controlled expansion) Al₂O₃ content (can be reduced appropriately)

Heavy-duty wear-type large-scale cement rotary kiln transition zone normal temperature compressive strength + bulk density wear resistance (separate test can be requested) apparent porosity (can be appropriately relaxed to 18%)

4. Practical suggestions: Ask three more questions when choosing bricks

The next time you communicate with a supplier, don"t just ask "how much". You can try asking three more sentences:

"Can you provide the measured data of thermal shock resistance for this batch?"

If the other party is hesitant, it means that they either haven’t tested it or the data doesn’t look good.

"With the same Al₂O₃ content, what is the main difference between your bricks and other bricks?"

It depends on whether the other party is bragging about the origin of the raw materials, or whether they are talking to you about particle gradation and binder systems. The latter is more reliable.

"Are there any operating cases similar to ours? How long did it take?"

It is necessary to have specific kiln shutdown inspection records, not general "customer feedback is very good".

5. Summary

When choosing integrated furnace bricks in 2026, you can change your thinking:

From "Look at the report and select the brick" to "Look at the working conditions and select the brick".

You should look at the Al₂O₃ content, but don’t stare at it. Pay more attention to thermal shock resistance, volume density, and reheat line changes, which are the indicators that really affect the service life on site. A detailed physical and chemical index test report is more effective than a hundred sentences "Our bricks are of good quality".

If you happen to have brick samples on hand to select, or are not sure about a certain indicator, please follow our subscription account and leave a message, and our engineers will select the model for you.

This article was generated with AI assistance and reviewed and published by Shengyuan Refractory Materials Technology Center