PRODUCT DESCRIPTION

Fused Cast AZS Blocks Introduction

Fused Cast AZS block, also known as electrofused zircon corundum block, is a high-performance refractory material primarily used to construct glass melting furnaces. The acronym AZS stands for its three main chemical components: Alumina (Al₂O₃), Zirconia (ZrO₂), and Silica (SiO₂).

Production Process

Unlike sintered bricks that are bound together by pressure and sintering, fused cast AZS blocks are manufactured using a foundry-like process:

1.High-purity alumina powder and zircon sand (composed of 65% zirconia and 34% SiO2) are mixed together.

2.The mixture is melted in an electric arc furnace at extremely high temperatures more than 2000°C.

3.The molten liquid is cast into various molds and slowly cooled down to create a white solid with a dense, tightly locked crystalline structure and near-zero apparent porosity.

Casting Methods

Fused cast AZS blocks are classified and selected not just by their chemical composition, but primarily by their casting methods. During the cooling process, liquid AZS contracts significantly, leaving a huge shrinkage cavity inside the block.

To manage this cavity, we use four distinct casting methods, each offering specific operational advantages.

Normal Casting (PT)

The liquid batch is poured directly into the mold and cooled as-is. The shrinkage cavity forms naturally in the middle of the non-working face.

Advantages:

Lowest Cost: The most economical manufacturing process with zero material waste.

Excellent Thermal Shock Resistance: The internal void provides space for thermal expansion, reducing the risk of cracking during furnace heat-up.

Best Used For: Areas completely out of contact with liquid glass and under low erosion, such as the superstructure of the furnace or crown walls.

Tilt Casting (QX)

The mold is tilted during the casting and cooling process. This forces the shrinkage cavity to shift away from the center and into one specific rear bottom side of the block. One complete dense zone forms at the opposite end.

Advantages:

Cost-Effective Defense: Cheaper than completely void-free blocks, but offers a perfectly dense working face.

Targeted Longevity: By installing the dense side facing the molten glass and the cavity side facing outward, it delivers excellent erosion resistance.

Best Used For: Furnace sidewall or upper sidewalls where only one face encounters aggressive chemical attacks.

End Casting (ZWS)

An extra riser is attached to the top of the mold. The shrinkage cavity forms entirely within this riser. Once cooled, this top portion is sawed off, leaving shallow shrinkage cavity at the very edge where it was cut.

Advantages:

High Structural Density: Over 90% of the block is completely solid, offering massive resistance to physical and chemical wear.

Extended Furnace Life: Prevent the block from breaking too early when melted glass erodes through to an shrinkage cavity inside.

Best Used For: Glass-contact sidewalls, and areas experiencing heavy liquid currents.

Void-Free Casting (WS)

Similar to End casting, but uses a much larger riser. The top riser is cut off completely, leaving no shrinkage cavity in bricks.

Advantages:

Maximum Corrosion Resistance: No voids or loose crystal structures for molten glass to penetrate.

Zero Joint Leakage: Can be machined and diamond-ground to extreme tolerances for tight, leak-free joints.

Best Used For: The most critical and aggressive zones of the furnace, including the throat, doghouse corners, dam blocks, and bubbler blocks.

Key Characteristics

Fused cast AZS blocks are highly regarded in glass industry due to their distinct microstructural properties:

l Chemical Composition: Fused cast AZS blocks consist of Alumina (Al₂O₃) for high-temperature stability, Zirconia (ZrO₂) for ultimate corrosion resistance, and Silica (SiO₂) to form a filling glass phase between crystals.

l Near-Zero Porosity: The melting process yields a dense, tightly locked crystalline structure with an apparent porosity of less than 1.2%.

l Superior Corrosion Resistance: it resists the severe destructive, chemical erosion caused by moving molten glass liquid and aggressive alkaline vapors.

l Thermal Stability: They maintain structural integrity under extreme heat exceeding 1500°C to 1600°C.

l High Mechanical Strength: Its dense, void-free crystal structures withstand high physical abrasion and structural creeping at high temperatures.

l Low Glass Contamination: Adopt oxidation processes to minimize impurities that could cause bubbling or defects in final glass products.

The Three Main Grades

Fused cast AZS blocks are universally classified into AZS 33, AZS 36 and AZS 41 by the percentage of Zirconia (ZrO₂) content, which determines their level of corrosion resistance and application part inside the glass furnace.

► Fused Cast AZS SR-AZS33

Description

Fused cast AZS SR-AZS33 block is the most widely used and cost-effective fused cast material in glass melting furnaces. Characterized by a Zirconia (ZrO₂) content of approximately 33%, it is primarily used in zones with moderate glass liquid corrosion or in areas without direct glass contact.

The performance of the SR-AZS33 stems from its unique three-phase interlocked microstructure, which is formed during high-temperature melting followed by controlled cooling. It ensures its great resistance to glass liquid.

Corundum Phase (α-Al₂O₃): Approx. 47%. This phase provides high mechanical strength and structural hardness.

Baddeleyite Phase (ZrO₂): Approx. 32%. These tiny, columnar crystals wrap around the corundum crystals, acting as the primary shield against chemical erosion by molten glass.

Vitreous Phase (SiO₂-Al₂O₃-Na₂O): Approx. 21%. It acts as a "buffer matrix" filling the interstitial spaces between crystals. By absorbing the volumetric expansion during heat-up, it grants the block the best thermal shock resistance among all AZS grades.

Advantages

1. Superior Thermal Shock Resistance: Because its vitreous phase content is slightly higher than that of the 36# and 41# grades, it exhibits the highest resistance to cracking within the critical crystal phase transformation range (900°C - 1100°C).

2. Maximum Cost-Efficiency: It does not require expensive desiliconization processes or pure chemical zirconia powder. This lower production cost makes it ideal for large-scale installation.

3. Minimal Glass Contamination: Modern manufacturing utilizes an oxy-fuel melting process to minimize gas-producing impurities. This ensures that the blocks cause virtually zero bubbling or stone defects in the final glass product.

Application

The choice of block depends heavily on its casting method.

1. Normal casting (PT) block is primarily used in non-glass-contact areas of the furnace superstructure, such as crown, breast walls, tuck stones, port crown, doghouse crown and feeder arches.

2. Void-free or End-cast (WS or ZWS) blocks are widely chosen for glass-contact areas such as melting tank corners, working end sidewalls, paving blocks, feeders, and forehearth channels where long-term stability and leak prevention are required at an optimized budget.

   TECHNIQUE DATA