Foundry Tooling — What Is a Riddle Used For? In sand moulding practice, identify the primary use of a riddle during mould preparation and sand handling.

Introduction / Context:
Foundry tools have specific functions. The term “riddle” refers to a sieve used to condition moulding sand by removing lumps and foreign matter, thus improving surface finish and reducing defects.

Given Data / Assumptions:

• Green sand moulding method.
• Need for uniform, fine sand to face the pattern and cavity.
• Objective is defect prevention and easily collapsible sand.

Concept / Approach:
Passing facing sand through a riddle reduces large particles and debris that could mar the mould surface, cause erosion, or embed in the casting. Clean, uniformly graded sand improves permeability and reduces inclusions.

Step-by-Step Solution:
Identify the tool: a riddle is a sieve.Apply its function: removing lumps and contaminants from moulding sand.Conclude its primary use is cleaning/conditioning sand before ramming.

Verification / Alternative check:
Standard foundry practice specifies riddled facing sand near the pattern for improved surface quality.

Why Other Options Are Wrong:
Smoothing/depression cleaning uses slicks and trowels.Moistening is done with water spray or swab, not a riddle.Reinforcement relates to gaggers/chaplets, not riddles.

Common Pitfalls:
Skipping riddling leads to rough surfaces and sand inclusions.

Final Answer:
cleaning the moulding sand