Maximum volumetric shrinkage during firing of dried refractories: approximately how high can the shrinkage be in severe cases?

Introduction / Context:
During firing, dried refractory shapes densify as pores close and bonds form. Linear and volumetric shrinkage depend on composition, particle size distribution, and firing schedule. Understanding upper-bound shrinkage helps in setting allowances and mould sizes.

Given Data / Assumptions:

• Shrinkage discussed here is volumetric after drying, during firing.
• Worst-case shrinkage may occur in fine, plastic, high-clay mixes.
• Figures are approximate guidance.

Concept / Approach:
While typical linear shrinkage might be a few percent to low double digits, volumetric shrinkage can be substantially larger. In severe cases—fine-bodied, highly sinterable formulations—volumetric shrinkage up to roughly 30 percent has been documented. Such cases require careful mould oversizing and controlled firing to prevent warpage and cracking.

Step-by-Step Solution:
Recall relation: volumetric shrinkage ≈ 3 × linear shrinkage (approximate).Consider highly sinterable bodies with glassy phases → larger shrinkage.Identify 30 percent as an upper-bound figure used in practice.

Verification / Alternative check:
Manufacturing manuals caution about large volumetric shrinkage in plastic-bonded bodies, citing values approaching 30 percent under aggressive firing schedules.

Why Other Options Are Wrong:
5–20 percent: common for many products, but the question asks maximum in severe cases.

Common Pitfalls:
Confusing linear with volumetric shrinkage; the latter can be much higher numerically.

Final Answer:
30 percent