Hearth versus shaft furnaces—classification check Which of the following is NOT classified as a hearth-type furnace used for heating or melting on a refractory hearth?

Introduction / Context:
Furnaces can be broadly categorized by geometry and how the load is supported and heated. Hearth furnaces use a refractory hearth where material rests and is heated above. Shaft (stack) furnaces operate with a vertical burden and counter-current gas flow. Knowing the class helps predict operation and heat-transfer behavior.

Given Data / Assumptions:

• Typical industrial furnaces for steelmaking, glass melting, and reheating are considered.
• Definition: hearth = horizontal refractory base; shaft = vertical packed burden.

Concept / Approach:
Glass tank, open-hearth, and reheating furnaces are hearth types. A cupola is a vertical shaft furnace for cast iron, operating with coke and air blast, not a hearth furnace. Therefore, the exception is the cupola.

Step-by-Step Solution:

Verification / Alternative check:
Process schematics show cupola burden charged from the top; product iron is tapped at the bottom—typical shaft operation.

Why Other Options Are Wrong:

• Glass tank furnace: molten glass pool on a hearth.
• Open-hearth furnace: steelmaking over a refractory hearth.
• Reheating furnace: stock rests/moves over hearth or beams.

Common Pitfalls:
Confusing blast furnace and cupola with hearth designs due to both being melt units; geometry and flow direction are the key differences.

Final Answer:
Cupola