Ramming masses in furnace construction: they are used for what purpose in refractory linings and maintenance?

Introduction / Context:
Ramming masses are unshaped refractories installed by pneumatic or manual ramming to form dense, jointless linings. They are essential where monolithic continuity is advantageous, such as induction furnace working linings, tap holes, spouts, and localized repairs. This question checks awareness of their dual role in both new construction and maintenance.

Given Data / Assumptions:

• Ramming mixes are supplied as graded refractory aggregates with binders.
• Installation by ramming compacts the mix, minimizing joints and cold faces.
• Service conditions may be thermal, mechanical, or chemical.

Concept / Approach:
Because ramming produces a contiguous monolithic body, it is ideal for obtaining smooth, jointless working faces that resist infiltration and erosion. The same property makes ramming mixes effective for patching and rebuilding worn furnace sections without dismantling entire brick courses. Hence, both creating monoliths and performing repairs are valid and common uses.

Step-by-Step Solution:
Identify monolithic need: jointless working face desired → use ramming mass.Identify repair need: localized erosion/slag attack → rammed patches restore profile.Conclude that both (a) and (b) apply.

Verification / Alternative check:
Industry practice in induction furnaces and foundries shows silica or alumina ramming masses for working linings, while basic ramming masses are used for repair of basic zones in steelmaking equipment.

Why Other Options Are Wrong:
Only (a) or only (b): artificially restrict actual practice.Neither: contradicts standard installation manuals.Cold insulation only: conflates insulating castables with dense ramming masses.

Common Pitfalls:
Assuming ramming masses are the same as castables; they differ in installation and properties.Overlooking dry-out and sintering steps needed to achieve final properties.

Final Answer:
Both (a) & (b)