For annealing furnaces (walls, roofs, and combustion chambers), which refractory brick class is commonly specified to handle the moderate service temperatures and cycling?

Introduction / Context:
Annealing furnaces typically operate in moderate temperature ranges (often below the extreme temperatures of smelting or steelmaking). Refractory selection balances cost, thermal shock, and chemical compatibility. This question focuses on the standard lining choice for walls, roofs, and combustion chambers in annealing service.

Given Data / Assumptions:

• Service: annealing (moderate temperature, controlled atmosphere).
• Need: adequate refractoriness plus reasonable cost and thermal shock tolerance.
• No highly corrosive slags or extreme flame impingement conditions assumed.

Concept / Approach:

High-duty fireclay bricks (alumino-silicate) provide sufficient refractoriness and mechanical strength for many annealing applications and are cost-effective. Silica bricks are optimized for very high, steady temperatures (domes/crowns), and mullite or SiC bricks are used when higher temperature strength, abrasion, or special atmospheres demand them—often at higher cost.

Step-by-Step Solution:

Verification / Alternative check:

Industry practice and specifications commonly list fireclay bricks for general-purpose furnace linings in annealing service.

Why Other Options Are Wrong:

Silica: Better suited to very high-temperature crowns with low thermal shock; over-specified here. Mullite/SiC: Higher performance and cost; chosen when specific stresses require them.

Common Pitfalls:

Defaulting to the most refractory brick, ignoring cost-performance optimization for moderate service.

Final Answer:

High-duty fireclay bricks