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AZS Bricks: Indispensable Refractory Materials for Modern Glass Furnaces

2026-06-25 08:56 Chaoyu Refractory Technical Team

Glass furnaces operate under extreme harsh working conditions, including continuous ultra-high temperature up to 1850°C, severe chemical erosion from molten glass, frequent thermal shock caused by temperature fluctuation, and long-term liquid scouring. Refractory lining materials directly determine the service life of glass furnaces, production stability and finished glass quality. Fused cast AZS (Alumina-Zirconia-Silica) bricks have become the dominant refractory lining material for float glass, container glass, borosilicate glass and other industrial glass furnaces worldwide, thanks to their ultra-high density, excellent molten glass corrosion resistance and low contamination characteristics. This article systematically introduces the chemical composition, manufacturing process, core physical and chemical properties, mainstream grade classification, targeted furnace zone applications, operation maintenance strategies and future development trends of AZS bricks, providing professional references for glass furnace design, refractory selection and daily production management.

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1. Introduction

The glass manufacturing industry is a typical high-temperature industrial sector that relies heavily on high-performance refractory materials. Inside a glass melting furnace, raw materials are melted into homogeneous molten glass at temperatures ranging from 1500°C to 1850°C. The flowing alkaline molten glass will continuously erode the furnace lining, while periodic furnace temperature adjustment and production shutdown trigger drastic thermal expansion and contraction of refractory bricks. Traditional refractory materials such as high-alumina bricks and silica bricks cannot withstand long-term composite damage of chemical corrosion and thermal shock, leading to short furnace campaign life, frequent maintenance and increased glass defects including stones, cords and bubbles.

Developed based on alumina-zirconia-silica ternary eutectic system, fused cast AZS bricks break through the performance bottleneck of conventional refractory products. With a compact microstructure formed by electric melting and integral casting, AZS bricks perfectly balance high-temperature structural stability, corrosion resistance and thermal shock resistance. At present, more than 90% of large-scale industrial glass furnaces adopt AZS bricks as key lining materials for melting tanks, glass line areas, throats and forehearths, greatly extending furnace campaign life from 3-4 years to 8-12 years and reducing overall production costs for glass enterprises.

2. Basic Composition and Manufacturing Process of AZS Bricks

2.1 Chemical Composition

AZS bricks are composed of three core raw materials: alumina (Al₂O₃), zirconia (ZrO₂) and silica (SiO₂). The synergistic effect of three components endows bricks with comprehensive high-temperature performance:

Alumina (Al₂O₃): Acts as the rigid skeleton of AZS bricks. With a melting point of 2050°C, it provides excellent mechanical strength and high-temperature structural stability, preventing brick deformation under long-term high-temperature load and flame impact.
Zirconia (ZrO₂): The core functional component resisting molten glass erosion. Zirconia features ultra-high chemical inertness against alkaline molten glass, and its phase transformation can absorb thermal stress to improve thermal shock resistance. Higher zirconia content means stronger corrosion resistance.
Silica (SiO₂): Forms a small amount of uniform glass phase inside bricks to bond crystal phases tightly. Moderate glass phase optimizes the compactness of bricks, while excessive glass phase will increase the risk of glass exudation and pollute molten glass.

2.2 Fused Cast Manufacturing Process

Different from ordinary sintered refractory bricks, AZS bricks adopt full electric melting and integral casting process, which is the key to its superior performance. The complete production flow is as follows:

Raw material batching: High-purity alumina powder, zircon sand and silica powder are proportioned accurately according to different AZS grade standards.
Electric arc furnace melting: Mixed raw materials are heated to above 1900°C in an electric arc furnace to form homogeneous molten liquid without internal pores.
Integral casting: High-temperature molten liquid is poured into customized moulds for one-time integral forming, avoiding layered structure inside bricks.
Annealing treatment: Slow and staged annealing eliminates internal residual stress generated during rapid cooling, preventing brick cracking during subsequent high-temperature service.
Finishing and inspection: Surface cutting, size calibration and strict physical and chemical performance testing before factory delivery.

This fused cast process makes the apparent porosity of qualified AZS bricks lower than 0.8%, far denser than sintered refractories, and effectively blocks the penetration of molten glass into brick interiors.

3. Mainstream AZS Grades and Performance Comparison

According to zirconia content and glass phase proportion, commercial AZS bricks are divided into three mainstream grades: AZS 33, AZS 36 and AZS 41. Their composition, performance and applicable scenarios vary significantly, as shown in the table below:

Grade	Al₂O₃ (%)	ZrO₂ (%)	SiO₂ (%)	Glass Phase (%)	Max Service Temperature	Core Advantage
AZS 33	32-35	32-35	14-17	18-22	1700-1750°C	Cost-effective, excellent thermal shock resistance
AZS 36	47-50	32-35	13-15	15-18	1750-1780°C	Balanced corrosion resistance and cost, universal grade
AZS 41	45-48	40-42	11-13	10-13	1780-1850°C	Strongest corrosion resistance, lowest glass pollution

With the increase of zirconia content, the internal glass phase content decreases gradually. Higher zirconia content enhances anti-erosion performance, while lower glass phase reduces the risk of glass phase exudation, which is critical for producing high-purity optical glass and solar glass.

4. Targeted Application of AZS Bricks in Different Glass Furnace Zones

Different areas inside glass furnaces bear different temperatures, molten glass erosion degrees and flame impacts. Reasonable matching of AZS grades according to working conditions can maximize furnace service life and control refractory investment cost precisely.

4.1 AZS 33: Non-molten-glass contact areas

As the most economical grade, AZS 33 is applied to furnace superstructure areas without direct contact with molten glass, including breast walls, charging port sidewalls, regenerator checker bricks and high-temperature flues. These areas face drastic temperature changes rather than severe glass erosion, so the excellent thermal shock resistance of AZS 33 can fully meet operation demands while cutting material costs.

4.2 AZS 36: Conventional key erosion areas

AZS 36 is the most widely used universal grade, suitable for melting tank sidewalls, furnace throats, forehearth channels and flame impact zones. It balances corrosion resistance and production cost perfectly, and is the preferred lining material for most soda-lime container glass and ordinary float glass furnaces.

4.3 AZS 41: Severe erosion and high-purity glass production areas

With the highest zirconia content and minimum glass phase, AZS 41 is used for the harshest furnace zones: melting tank hot spots, bubbling areas, electrode holes and dead corners with strong molten glass scouring. It is also mandatory for high-end glass production lines such as borosilicate glass, optical glass and photovoltaic solar glass, as it can effectively avoid glass defects caused by refractory pollution.

5. Core Advantages of AZS Bricks Compared with Other Refractories

Superior molten glass corrosion resistance: Inert zirconia component resists alkaline molten glass erosion effectively, with erosion rate less than 1/5 of traditional high-alumina bricks.
Ultra-low glass contamination: Compact structure reduces brick peeling and glass phase exudation, greatly lowering the occurrence rate of stones, bubbles and stripes in finished glass.
Excellent thermal shock stability: Zirconia phase transformation absorbs thermal stress, adapting to frequent furnace temperature fluctuation without cracking or peeling.
Long service life: Integral fused cast structure avoids internal pores, realizing stable long-term operation under continuous high temperature.
Self-protective skull formation: Under external air cooling, a thin solid glass layer (skull) will form on the inner surface of AZS bricks, isolating bricks from direct contact with flowing molten glass and further slowing down erosion.

6. Daily Operation and Maintenance Tips for AZS Brick Linings

Although AZS bricks own outstanding comprehensive performance, standardized operation and maintenance are essential to extend furnace campaign life:

Follow strict heating-up curve during furnace startup; avoid rapid temperature rise to prevent thermal stress cracking of annealed AZS bricks.
Stabilize furnace operating temperature; avoid long-term over-temperature operation exceeding the maximum service temperature of matched AZS grade.
Keep stable external air cooling for melting tank sidewalls to maintain complete protective glass skull.
Reduce frequent furnace shutdowns and temperature fluctuations; each drastic cooling-heating cycle will cause irreversible damage to refractory linings.
Conduct regular thermal imaging inspection on furnace sidewalls to detect local thinning of bricks and hidden erosion risks in advance.

7. Development Trends of AZS Refractory Technology

With the upgrading of glass industry toward large-capacity furnaces, high-efficiency melting and high-purity glass production, AZS brick technology is developing in three directions: first, low-glass-phase ultra-pure AZS products to further reduce glass contamination for high-end optical and electronic glass; second, micro-pore optimized AZS bricks with better thermal insulation performance to reduce furnace energy consumption; third, composite AZS refractory structures combining dense cast layers and insulating layers to realize integration of anti-erosion and heat preservation. In addition, green low-carbon production processes for fused cast AZS bricks are being promoted to lower energy consumption during brick manufacturing.

Chaoyu Refractory http://Chaoyu Refractory Technical Team

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