Grinding of molding powders, waxes, resins, and gums: which mills are commonly used for these relatively soft or thermoplastic materials?

Introduction / Context:
Processing molding powders, waxes, resins, and gums often requires coarse-to-medium size reduction without excessive heat build-up or contamination. Impact-type mills are favored for such friable or thermoplastic materials when appropriate cooling is provided.

Given Data / Assumptions:

• Materials are comparatively soft, sometimes thermoplastic.
• Objective is controlled impact breakage, sometimes with cooling.
• Product sizes are typically in the sub-millimeter to few-millimeter range.

Concept / Approach:
Hammer mills provide high-speed impact suitable for brittle or soft materials, while cage mills (multi-row impact mills) also achieve effective breakage by repeated impacts between rotating cages. Both can be outfitted with screens and airflow to manage temperature rise and prevent melting or sticking.

Step-by-Step Solution:
Identify impact mechanisms suitable for soft/thermoplastic feed: hammer and cage mills.Note need for temperature control: chilled air or cryogenic aids as needed.Conclude both mill types are used in practice.

Verification / Alternative check:
Industrial catalogs list hammer and cage mills for resins and waxes with ancillary cooling and classification to avoid agglomeration.

Why Other Options Are Wrong:
Choosing only one ignores wide practice; both are established choices.“Neither” contradicts standard usage in plastics and chemicals.

Common Pitfalls:
Running thermoplastics without cooling; heat softening leads to smearing and screen blinding.

Final Answer:
Both (a) & (b)